Swapping a Slant 6 for a V8

If your going to do an engine swap go big or go home. 440 is my vote, all the same work to do the swap.
BUT as 318willrun pointed out it really depends on what you are trying to do with the car. If you have never done this before, a stock engine and trans from a donor car would be the safest way to go. You get all the misc bits, driveshaft, mounts, cross members, nuts and bults etc.