Magnum Swap Checklist...... this is a long one.....

Might rethink the head gasket thickness. Iirc the magnum pistons stick out of the hole .020 I went with a felpro 520SD or SD520. I can't remember now. Has a compressed thickness of something like .054. You'll need it to get piston to head clearance.

They were .060 or so in hole on my 96 5.9 Magnum.