If you're talking about the transmission cover that contains the water pump and oil filter mount, they both have the same bolt pattern, and will interchange. The only difference is the neutral switch - it's in the engine case on the '80 and '81, and in the transmission cover on the '82 and '83. If yours is an '81 engine, and you want to use an '82 cover, you need to fill the cutout in the cover where the switch wire would normally pass through.