What parts??? Body, engine, suspension???
It is listed in the 1991 Pontiac Firebird Operations Manual
A wiring diagram, for a 1991 Pontiac Firebird, can be obtained from most General Motors dealerships. The wiring diagram can also be found at most auto-parts stores.
I calc'ed my '91 V8 Formula Firebird to be about 18 mpg.
i know the backs are 6x9
A firebird can't "have" third gen. It either is or is not a third generation firebird, and Yes, a 1991 is a third generation.
underneath the drivers door
If they are both Chevy V8 cars it will bolt up.
I use 10W-30
I know mine is on the drivers side there is a door in the kick panel
the main vin plate should be mounted on the dash where you can see through the windshield. it should also be on a sticker in the door jam on the drivers side. and on my 1991 firebird it has the vin printed on all the stock windows.
I have a 1990 Pontiac firebird, and the gap on that, I believe is .035. If you still have the sticker under your hood with the engine size, it says it right on there.
10w30 motor oil should work nice