Flat head blocks ?

[Bob NH]

I'm sure this has been thrashed to death before but looking for a little input ? A fellow I know wants to know if I am interested in about three flat head blocks that he has had quite some time and I think he said the cranks are there also. I told him what little I knew about favorite places to find cracks, along the pan rails, between valve chambers and cyl bores etc. How chancy is it taking a shot on these even if they appear good to the eye ? I read a lot about pressure testing etc. to find hidden surprises.