If you decide to get a 225 core and rebuild it, I'd stick with the '67 and older one. All of those have forged cranks. I'd try to find one that has been machined for the pilot bushing too. Some did, some didn't. All the manual trans applications did and most automatics didn't, but, some automatics had one too. Whatever was on the shelf at the time I guess! You can make a bushing for the unfinished crank or have it machined, but, that's just an added cost to avoid if possible. If you get a complete '66 and older engine, you also get the benefit of extra parts that will fit your car too......pan, mounts, brackets, carb, etc. It shouldn't be too hard to find one. Lots of V8 transplants out there with an extra /6 getting in the way under the work bench.