69 Barracuda Clutch Shake Help Needed.

A Hot Rod article indicates routine box use for factory 440, 426 H, and converts. But that includes b's and c's and does not mention anything pertaining to rear / fronts vs. rears only. I haven't really tried to find the rational on why one and not the other for my 383 4 spd. I expect it was a build cost factor and if it don't need it don't do it sort a deal.