[Your comments in quotes.]
"What tools can we use, if any, to actually see the position of all the uncials on a variant?"
One usually has to do a fair bit of digging. The INTF's New Testament Transcripts is a good place to start:
There is also ITSEE for texts of John's Gospel:
The data I have comes from a variety of sources, as outlined in the Sources section of my Views site:
"Tim, what do you use to be sure you have all the uncials placed right?
Or do you have to calculate and extrapolate as above ? (It sounds like you might use a computer collation, but it is not totally clear if there is any different than the written one, that lacks many of the Byzantine majority uncial listings and forces you to do some special checking and guessing)"
I use a number of modes of multivariate analysis (PAM, CMDS, DC). Each mode operates on a distance matrix. Each mode places the witnesses in its own way. CMDS gives you the best possible representation (according to its stress function) of distances between witnesses with the specified number of dimensions. (I specify three.) All I do is apply established multivariate analysis techniques to distance matrices derived from New Testament textual data. The data sets are always samples of one kind or another. (Even if I had a complete set of all readings of all extant NT witnesses, it would still be a mere sample of what once existed.)
"Is there a nice explanation, are 1, 2, 3, 4 variant units or the major controls?
Can I know if Alexandrinus on Mark 1:1 is a specific variant ? Did I miss an Intro?"
The introduction to the (draft) Views site is probably the best place to start:
For more detail, see chapter two of my "Analysis of Textual Variation":
But the thing I would really like people to read is my Groups article: