Lyle - it's pretty straightforward.
After bringing the piston to TDC, remove the head on the damaged engine. Make a small mark on the piston crown and sleeve. Use this mark when reassembling to insure that the piston/sleeve are at the same position when inserted into the new case.
Remove the sleeve - slight heating with a heat gun may be needed. Disassemble the rod from the crank and then finish disassembly.
Clean all parts, apply oil to the moving parts and reassemble everything into the new case. Double check that the piston/cylinder marks are aligned.
You should not have to force anything - all parts should slide together smoothly.
If the backplate gasket is damaged, you can eliminate it using my sealant method as described in C/L World.
That's it. Tighten everything down, doing opposite screws on the head and you're in business.
Bob Z.