pull the whole thing out and buy a "350" from the salvage yard
This happens way too frequently: "buyer's remorse", when they look at the cost per HP and realize what a bargain even a used V8 is. You should only be considering this if you understand that this is not a cost-effective way to make the car fast (which is nitrous), but it's an excellent way to make it interesting, memorable, fun, and educational. You learn nothing by putting in a crate motor. I'm working on a 1937 Harley engine, which will probably never make more than 70 HP (original is about 38) instead of a shovelhead, blah because it hasn't been done and I'm inventing it as I go along.
