Has anyone ever put a s40 case on a s20? I have both my gears are shot in the s40 but I have a good gear set in a s20 but the case has a chunk missing it was dropped was just wondering if the case from the s40 would fit the s20.

 

Not possible.

You can use the S20 gears in the S40 case. You'll need to shim the mainshaft, swap the complete final drive over, use the S40 3/4 slider, and use the S20 mainshaft oil guide plate.