Check the numbers on the block to the 440 Source block page. A 75 block was built heavier, with thicker webbing, and reinforcements. 440 Source called them "Super Block". I picked up a block out of a motorhome for $125, got it home, checked the numbers and it came up "Super Block" by pure luck. I had it cross bolted on the mains. My builder said the bottom end shouldn't go anywhere. Said I could go with a supercharger with just a piston change. I suppose it all depends on what you want to do with it.