Another way to heat the T-nuts is to thread a longer bolt into it and heat with a propane torch. Tap the heated bolt with a hammer to loosen the T-nut.

Drill the old hole oversize (like 3/16 or 1/4") and glue in a wood dowel to eliminate it. A new hole can be drilled very close to the eliminated hole if need be.

Try and get the engine centerlines to match up, it'll look better.