Only potential problem I can see with a new crank is that the balancer gears *may* have to be replaced as well. Ford updated the balancer and crank drive gears for durability reasons, which might present a mis-match issue.
It's possible that an aftermarket crank uses the old style gear, in which case you may be OK. I'm going off of memory here, maybe Rod or Rick B can help, but I think the old gears were 1/2" wide, and the new ones were 9/16"? Or am I confusing those numbers with head bolt diameters?
If you were to get a new crank, you would be a fool to use the old bearings. It would be like buying a brand new pair of shoes and wearing them with dirty socks.
If you have the front end off already, removing the engine block will be fairly tame by comparison.