My engine started life as a black merc 6.2 and yes it's a 377 cu. motor will run all day on 87 in fact it will not run any better on 89-93. It should have a forged steel crank but does have the hyper. pistons good solid engine for what it is, prop this engine to turn 4,900 RPM's that's about where it runs out of power it will spin to 5450, limiter says 5200 but it's a soft limiter but again no news to spin it past 4900 just prop it there and you'll be better off.
Steve
2006 CLASSIC 18 WHIPPLED MX 6.2, BRAVO 1, STAINLESS MARINE EXHAUST, LATHAM STEERING, IMCO 2" SHORTY, LABBED MIRAGE PLUS
TALK IS CHEAP, I'M FROM THE "SHOW ME STATE" SHOW ME