440
Cases are pretty much the same. Look at the stroke of the crank that you are using. When I did my 660, I had a almost new 440 crank that we picked up at the swap meet. I got it all together and the pistons hit the head. Had to have the original 600 crank rebuilt. Carl's used to do a exchange on the new style small block 600 cylinders not the 440s. You had to send your 440s in and wait for them to be machined. You will need to check with them to see if they still do that. I believe the newer style 440 has the same stroke as the 600 so your bottom end should work. You may need some minor machine work on the top case half to clear the bigger pistons on a 660. They reflash the CDI for you as well as cutting the head and exhaust valves.
