To follow up, I visited the Harry Ransom Center at the University of Texas at Austin, where I was able to view the Rafael Sabatini Papers last week.
 
Since my visit took place during a family vacation (much to the consternation of my wife, who, despite being married to a librarian, doesn't consider library research to be a fun vacation activity), I only had time for a cursory and not very scholarly examination of the material: my goal was simply to assess the collection and determine how much time I might need for future "non-vacation" activity. For anyone who is interested, I am copying and pasting some of my notes and observations, which, admittedly, don’t add very much to that which is already available.

(I apologize in advance if the formatting doesn't translate.)
 
The entire collection is contained in a single 15X10X5 archival container, subdivided by two sections (Series I: Works, 1909; Series II: Correspondence, 1912-1935) and 9 folders. The finding aid can be viewed at: http://www.lib.utexas.edu/taro/uthrc/00432/00432-P.html
 
Works, 1909

Item(s): “The Vintage Ale” (poem, 1909), typescript draft and finished booklet

The so-called “typescript draft” of this poem is bound. Is this really a specially-published volume? On the title page:
 
The Vintage Ale
A Riparian tragedy
 
Culled from the Log of the H.B. “Doralie”
 
The N.B.G. Press
L’ham 1909
 
It is addressed as follows:
 
To Harold Lee, ESQ
On the occasion of the dinner offered him by some friends of the H.B. “Doralie” at the Liverpool Junior Reform Club
Saturday, January the 23rd 1909
This Doggerel is Dedicated by Him Who Sorrows At His Absence

The first part of the poem:
 
The Argument.
Now this is the tale
Of a bottle of ale
Of a vintage most ancient and rare,
And of old Skipper Lee
Who with mariners three
Sailed the Dee in the “Doralie” fair.
 
The finished booklet seems to be some sort of commemorative program for the event, which contains the entire poem and some additional comments:
 
The Epic which follows, written specifically for the occasion by Mr. Rafael Sabatini, was declaimed during the evening by Mr. George Gilcriest. Despite that disadvantage, its beauties were not seriously marred—a striking tribute to the quality of Mr. Sabatini’s composition. It should be added that the hero of the Epic strictly denies its historical accuracy. But progress is not to be hampered in his flight; and Genius justly spurns, in its embellishment of a theme, the cold restrictions of unromantic fact.

Item(s): The Sacrament of Shame (unpublished play, undated), typescript draft

Title page:
 
The Sacrament of Shame
A Drama in three Acts
 
From Rafael Sabatini
27 Fitzjohns Avenue
Hampstead, London N.W. 3
 
A dramatization of The Romantic Prince. Act 1 takes place in “the hall of the house of Philip Danvelt”; act 2 takes place in “a room in the Ravenhof at Middelburg”; act 3 takes place in “an ante-room in the ducal palace at Bruges.” Play seems to incorporate most of the major characters from the novel, with the exception of the King of France. The name of the main character is Count Arnault of Aquitane, not Anthony of Edgmont.
 
Item(s): The Fortunes of Casanova (short stories, 1918), notebook, handwritten and typescript drafts

A bound notebook, mostly typed; several pages and most corrections handwritten.
 
Original title, typed, is crossed out:
 
The Great Comedian
Tales from Casanova
 
(replaced by Fortunes of Casanova)
 
Stories are:
 
1.       Augmentation of Mercury 2.       The Courier of Love (25 p) 3.       The Oracle (crossed out title: The Clavigula of Solomon) 4.       The Priest of Mars
The first page of the unpublished story, “The Courier of Love,” is entirely handwritten (as is “The Oracle”). I was unable to decipher most of the handwriting, including the first sentence. inquire about copying.. First sentences of the other stories are essentially identical, aside from some minor edits.
 
Item(s): King in Prussia (novel, 1944; published as The Birth of Mischief, 1945), handwritten notebook; The Life of Cesare Borgia of France (1911), Chapter XI: The Letter to Silvio Savelli, handwritten fragment with revisions; The Lost King (novel, 1937), typescript draft with revisions; The Sword of Islam (novel, 1939), typescript draft with revisions

All of the manuscripts have typed and handwritten revisions. Considerable time would be required for comparison to the published texts.
 
Series II. Correspondence, 1912-1935

Various letters to publishers; some private correspondence, personal notes. Handwriting is difficult to read.
 
Other collections containing Sabatini material:
 
Title:   Hesketh Pearson: An Inventory of His Papers
Matches:   Sabatini, Rafael,
1875-1950 --1.14    
 
Title:   Simmons B. J. and Co. Costume Design Records [HTML] 28%
Matches:   680 (a) Rylands, George, 1902- --211, 297 (t) Ryley, Madeleine
Lucette, 1868-1934--291 (a) Sabatini, Rafael, 1875-1950--351, 833, 902 (a)
Sachs, Maurice, 1906-1945--681 (t) Sacks, Joseph Leopold--426,    
   
Title:   John Lane Company:An Inventory of Its Records
Matches:   Sabatini, Rafael, 1875-1950--42..4Martin Secker (Firm) (Rafael
Sabatini)--30.6    
   
Title:   William A. Bradley Literary Agency:An Inventory of Its Records
Matches:   Sabatini, Rafael, 1875-1950 -- 54.3
 
Bradley:
Letters in French and English concerning French language translations of The Gates of Doom, Bellarion, The Sea Hawk, and Scaramouche.
 
Lane/Hesketh:
Various correspondence mentioning Sabatini, some works. Nothing of note.
 
Simmons:
The B. J. Simmons collection contains costume design drawings and materials related to productions of two of Rafael Sabatini's plays, and one film. An index of the collection can be found on the Center's web site at http://www.hrc.utexas.edu/research/fa/bjsimmons.folder.html and includes the following for Sabatini:
 
In the Snare, Savoy Theatre, 1924: 46 items in box 72.4-6, and oversize box 526.3;
The Tyrant, New Theatre, 1925: 18 items, box 179.5, oversize box 366.1;
Christopher Columbus, David MacDonald / Gainsborough Pictures, Rank Film Organization, 1949: 206 items, box 189.5, oversize boxes 379.4-383.2, and flat files #s 1184 and 1216.
 
Material for In the Snare and The Tyrant consists mainly of complete and highly detailed costume sketches for each character. Names of characters seem identical to those in the original novel/short story. Of note re: The Tyrant: Borgia was played by Matheson Lang (http://www.imdb.com/name/nm0485851/) and Panthasilea was played by Isobel Elsom (http://www.imdb.com/name/nm0255695/).
 
Material for Columbus consists mainly of inventory and financial records (re: costume rental).

-David