I think you're on the right track. Regarding the "crate engine" approach. If you plan to start with nothing, in other words, you want a "TOTALLY" complete new engine, just be advised it will not be cheap. Someone will have to come up with an entire long block. That's the easy part. Then, they have to locate all of the tin, the valve cover, timing cover and oil pan. Next is all of the various fasteners. That takes a lot of time and effort. It's not something that's going to happen for say 2500-3500 dollars. Sure, a basic long block can be had for that, but people seem to forget about all the other details. That is of course you plan on using all of that from your present engine. If you want a "plug and play" approach, just be prepared to pay someone for their time, parts and effort.