Is there a difference between the reference 7950 and 7970 pcb? Also, are the pcb's on the two "reference" styled 7950, one with the centered fan and one with the blower style, the same? I am confused because a lot of water blocks say that they are for the 7950 and 7970. All that matters when mounting a water block is where the screw holes are right?
What you're trying to do is a bit vague in your description, but from what I understand the GPU is the same mount spacing, so if using a universal GPU block only, they are compatible (yes on the spacing). If using a full block, it's debatable because a lot of them come labeled as 7950/7970 compatible and some are specific model numbers to each respectively.
I don't know 100% for sure, but bet on that they are basically the same card starting out, have the same orientation, have the same RAM chip count, same hole spacing, and the same cooler designs. What could be different could be VRM count as well as size of them, other than that, there shouldn't be much more to it.