whats the difference between a 327 block and a 350 block, just the size of the bore and a different crank???

Bore is the same, crank saddles may be different depending on the year of the block.

so if I got a 67-69 327 block it could be a 350 with the correct crank?

Any 327 can be made into a 350 with the correct crank. If it's a small journal block you'll need a crank that fits the saddles. If it's a medium journal block you can use a standard 350 crank.