If your using the TH400 then the only difference is the tailshaft. Easy enough to swap out in most cases. Worst case you shorten a driveshaft.
If your planning on keeping the sm465 that is where things get a bit tricky. Cadco has a flywheel and the thing is a Heavy sob. It is also quite thick.
https://cad500parts.com/product-category/driveline/
Call them to make sure your getting the right stuff for the application
I had a Lakewood bell(opened up to the sm465's larger bore), 1/8" block protectior, adapter plate, the thick flywheel and from there it was a basic BBC 454 clutch. But I only had like 1/16" between the block protectior and the flywheel. A mini starter was needed also because the Cad starter nose would not fit inside the lakewood.
Plan on dropping $500-600 in cad co parts plus another $200 for a BBC clutch.Watch the tooth count on the ring gear or your going to need to play with the starter also.
I have had 3 500's and 2 472's in squares. I had my last 472(68High C) sitting in the shop and finally got rid of it this summer. Those Cad engines blocks love to drink and in a square plan on 6 and if your lucky 8mpg. They are fun in a mudtruck where you want that torque. But they do have issues with oiling, valves and everything is more expensive then a BBC. An LS is a much easier option especially if you want to keep the sm465. Bolt in deal with the parts to bolt the engine up to that sm465 about 1/2 the price of the cad stuff.