can any one tell me if you can use a mercery crank and pistons in a ford block I am in dire need of a new block cause mine cracked

 

Yes the blocks are identical - only thing different is crank and pistons. Con rods are the same as well as everything else.

One caution. Make sure to keep the main journal caps that come on the replacement block WITH that new block. If you use the ones from the old engine on the new, you'll need to have them align-bored.

edit to add: they are the same within each series - early (39-47) and late (48-54) The con rod journals changed between the two and the early Ford bore is 3 1/16" where the early and late Merc and late Ford are 3 3/16" bore.