Doc, if you want to play with 30s & 40s Mopars with a Hemi, you have to part with some money. Even building them yourself from a pile of parts is expensive.

The 50s Hemi motors have the same bellhousing bolt pattern as a small block Mopar, but the issue is the tail end of the crankshaft sticks out about 3/4" and the flywheel or flex plate bolts have to thread into the crank. Any adaptor needs to space the trans back, and still leave room to thread the bolts through either the flywheel or the flex plate and into the crank. Then, they have to provide a way to hold a starter and keep it in the proper position. Then, after all the design work, they have to get the thing made so they can sell it to you and still pay their bills.

If you don't want to spend the big bucks to have that Hemi, you can always drop in a small block. It only takes about $20 G to build a nice small block 30s or 40s Mopar, if you can do everything yourself. if you have the experience, the equipment, and the knowledge to do it all yourself, and you can work on it 40 hours a week, you may be able to get it built in a year, but probably closer to two years. If you have to hire it out, expect to pay someone's wages for those two years, and pay an up charge on the parts.

its nearly always cheaper to but an already built car and make a few modifications to suit your needs. Gene