2g Head and block

Ok..lets say I have two engines, one manual the other automatic. What is the difference, if any, between the heads and blocks from both engines? Just the head and block, nothing else. I have a manual engine and need a new block and I found one but from an automatic engine. I want to know if wether to buy it or keep on looking for a block from a manual engine.

The motor and head is the sam the tranny is the only thing different is the tranny.