Look at all the filler in the water jackets on that old pro stock block. The front water jackets on the deck don't line up, so you'll have to do some work there. I think you break into water when you grind the pushrod clearance also. Probably not a huge deal if it's gonna be a dry block/alcohol combo. A little more work if you need a cooling system.

I remember a magazine article years ago about a guy that had a sand rail/dragster that had a modified 400 low deck block to accept hemi heads. Ran it NA, but alcohol injected IIRC. They'd welded tubes in the valley for the inner head studs.