Schumacher mount fitment

Can use biscuit mounts on a 77 400 block or do you have to use spool mounts and obviously the spool k member? I have a 68 small block k member and the biscuit big block Schumacher kit but the mount boss on passenger side of the block is narrower, I have a 383 and boss is thicker and the mount fits normal. I am sure I could shim the mount but that may throw everything off?