"Kevin, You do not mention wha
"Kevin, You do not mention what state/city. So we don't know what part of the country you are in! With a cracked block, no doubt cold winter climate!
I'd suggest that if you end up with a new block/heads that you at least investigate the cost of adding a closed cooling system before any rust scale starts within the new engine.
As for a rebuildable core, you need nothing more than an automotive 4.3L engine core.... match casting number for best results!
Some had the counter-balance shaft.... some did not. Match accordingly.
You should be able to pick one up from an Engine Rebuilders Supply company. Find someone who is an expert and matching casting numbers, etc.
They can best help you!
."