For what it is worth, this is my opinion.
The idea that bearings from an engine which caught fire, has no visable oil on the dip stick, and no known history, are useable, is
.
Do some research and find a local shop with erperience rebuilding the 7M and can correctly mill the block and head for the MLS gasket install (how much material removed from the head & block, determine how thick of a gasket to use). Talk with them and get some ideas for the rebuild cost. Save up enough money to have the shop do a proper rebuild. Give the shop both engines and let them determine the best components, (block, head, crank, pistons,etc.) from the two engines, that can be used. Replace what can not.
If you take short cuts in an engine rebuild, you will be rebuilding that engine again.