Duster small block to big block engine mounts

Trans-Dapt makes SB to BB mounts for the A-body, but only for the 67- 72 biscuit type K-member (Engine Performance & Vehicle Customizing Products From Hedman | Hedman Performance Group). 73+ A-bodies have a spool mount K-member. One alternative to Schumacher is modifying your stock K-member: Make Your Own DC-K Frame

You might also try posting a want to buy ad for a set of the Schumacher mounts. I found a new/never used set of them locally on Craigslist.