I am only familiar with 325A thanks to the picture on Moxon's site.
Comparing the pictures (http://vandercookpress.info/images/325AH.jpg
. Though I can't see
how your rollers work, it looks like the 315 is almost a functional
mirror image of the 325A. So my question is, does the form have to be
off of the press bed when you ink the rollers? If so, then maybe you
do not need a trip lock. I'm sure someone who knows presses better
than I, can correct or confirm.