A v8 belhousing from a late '50s or early '60s truck will bolt up to the 250. It will not be a bolt up to the '46 crossmember. However if you can do a little fabrication you can probably make it work.
I bolted a v8 into a '48 pickup with that bellhousing by using a '54 crossmember. I don't know how close a '54 crossmember would be to what you have now.
Of course you would have to build side motor mounts for the front. I agree, rebuilding the 235 would be easier.
