The rebuilt heads by the PO may be somehwat moot if you had to do the VLAs like you said. Not firing on a cylinder while also losing no oil doesn't add up to compression to me, though I admittedly know far less that others here.

A solid Montero is always worth new motor, ir you are inclined to keep it as whole, as opposed to chunking down coin for new, or newer.

That all said, if you run it until it stops, I'd be interested on the complete roller...

Big Truck: 00, 3.5, Endeavor, 5-Spd drive line in hand!
Little Truck: 87, 2.6T I/C, MT, LSDs, Tonneau Top
Her Truck: 03, 3.8, 20th Anniv, 65k
Daughter's: 06 Eclipse, Keeping it Mitsu!
FSMs: MitsubishiLinks.com