Do you have a shop near you that does custom machining? A bell housing to engine adapter or a transmission to bell housing adapter should not cost more than a thousand dollars even at a high end shop. We do our own first out of plywood (much cheaper than aluminum) and then transfer to steel or aluminum. I had a sign over my desk in my old shop that stated, "We can mount a 450 Cummins on a skate board if you have the Cummins, the skate board, and cash". On my straight eight Buick the Dynaflow transmission parts are scarce and pricey so I made a Chevy to Buick bell housing adapter as 55 and newer Chevy engine/trans parts are nearly universal. I consider front bearing retainer bell housing hole size to be a non-problem as well as input shaft length or size.
Chevy bell housing to straight eight Buick adapter made with common parts and $600 lathe 40 years ago and still working:
Engine with Buick bell housing:
[img]https://i.postimg.cc/5QYg7nb0/Rueben-s-65-Buick-engine-adapter-008.jpg[/img]Perfect size 3" driveshaft used as mandrel through main bearing bores and bell housing bearing retainer hole
[img]https://i.postimg.cc/2bPh6mNk/Rueben-s-65-Buick-engine-adapter-011.jpg[/img]Buick now has Chevy bell housing:
[img]https://i.postimg.cc/7b3f7SgM/Rueben-s-65-Buick-engine-adapter-012.jpg[/img]
