K-member

In the late 70's to early 80's chrysler (direct connection) sold a big block k member for a bodies. I used one to put the big block in my duster. they still show up on ebay or at moparts.com once in a while. offhand, I'd say they have been going for around $350 plus motor mounts. There's something in the tech section at bigblockdart.com about making one too if you have access to a welder.