Ackkk - senior moment!
I already had data, but not recorded as GMC, duh.
The center-to-center tappet distance (between linked pairs) of the KB etc. hemi roller tappet is 2.000", which is (almost?) correct for the 235/261 stovebolt (the "normal" hemi and B/RB tappets are 1.800" apart). The GMC distance is probably slightly larger, so the slots etc. in the link bars will need elongating, etc.
