Note: there are two versions of shocks per page 6 on the attached pdf.
Perhaps the original was the first version (with the lower buffer in the sleeve) and
the replacement was version 2 with the lower buffer between the sleeve and the chassis (as vwnate suggested on post #4)?
https://www.startekinfo.com/StarTek/outside/12265/disc_2/program/Chassis/32-100.pdf
On your first photo on post #7, more of the rod is exposed and it looks as if there is enough space for a buffer to fit.