/6 K-Frame vs. V8 K
My understanding is the washer is 70-later thing or thereabouts. If you want to beef up the LCA pin tubes go ahead, but you will likely gain nothing changing to a V8 k-member because it is likely that none of the critical areas are different because it is likely to be a 318 k-member.
BUT, if you can get a 73-76 V8 k-member with spool mounts you can build a big block k-member out of it without needing Schumacher mounts...