Facing an issue with a cracked top case at the seam, the other side is perfect. Instead of replacing both, I wanted to find out if anyone has tried putting two different case halves together (same engine size). Thanks in advance for your responses.

Not without machine work. You'll need a line bore for sure. If you look at the money you'll spend on that, it might be cheaper to get a new case.

I would think you would need to have the barrel registers machined as well to keep them the same. Don't think it's worth it unless your doing a full machine job on the case.

No. With the usual caveat: you can do anything with money.