I have a little mystery here that I'd like help with.

I found a 1982 264 GL, VIN # YV1AX 454XC 111 7115 in the boneyard. Only, it had a B21F engine! I triple checked the VIN number, both on the firewall and passenger door frame; it was correct. I believe that the VIN # was correct and that the original engine was a V-6 replaced with a B21F. The engine in the car has a CIS fuel injection system and Idle Air Control Valve. Moreover, the engine was poorly installed: two exhaust bolts were missing washers; the head bolts were not tightened to specs (I easily loosened all of them with only a 12" breaker bar); all exhaust manifold gaskets were inverted and did not align correctly with the exhaust manifold; the top of the cylinder head, where the valve cover sits, was immaculate. Either Inga the Swede had an off-day in Torslanda with assembling that engine or a local mechanic put it in.

Any guesses on how old/miles the B21F engine is? I'm wondering how long the 1982 RPV V-6 engines lasted (eg 100k miles) and what common causes of death are.