My buddy picked up a Laycock/Gear Vendors OD unit from ebay a couple of years ago for about $700 with shipping. It came with an adaptor for a Ford gear box. However he wanted to use it with an SM420. We went to the Gear Vendors shop and got the necessary adaptor, a shaft, and I believe some electrical components. The additional parts came to almost $900 and they don't give any discounts. It worked fine in the truck but kind of pricy in my view. A driveshaft mod was also required which was about $150.
As Jerry states the key would be to have some machine tools to make some of this stuff it could be more reasonable.
Fred


1956 3100 Pickup/Red/350/3sp OD/PS/Disc Brakes
1957 Bel Air Sport Coupe/Red/355/TH350/PS/Disc Brakes
2017 Silverado LT Single Cab SB/Black/5.3/6 Speed Trans
1947 Willys CJ2A w/F-Head engine