Reducing duration and lift is ordinary business.
What is pretty much permanent (only very small changes possible) is LSA.
Depending on whether the flanks are convex or not (both were used) it may have enough material to regrind for a flat tappet. If "hollow ground" I would guess not.
The roller tappets should have a link distance around 2" + some wiggle, may have been adapted from GMC (same tappet diameter, different tappet spacing).
Buick L8 also?
Common auto tappets were probably adapted by bushing the tappet bore down to .904" (Chrysler, AMC), .875" (Ford), .842" (GM). More about this on my page here:http://www.victorylibrary.com/mopar/roller-adapt.htm