If you are talking about you ECM( the computer that runs the engine) it is under the dash on the pass. side. You will need a 7mm socket to take the under dash paneling off before you see it
Any size SBC engine will fit and is compatible with a 91 Firebird. A 350 engine is the most common that is used for installing in a 91 Firebird.
have someone check the icm (idle control motor)
I calc'ed my '91 V8 Formula Firebird to be about 18 mpg.
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.
700r4
on the transmission tailshaft housing
Best way to do it is either a flatbed or a trailer
it should be on the door lock motor on some early '91 models
Disconnect wires at antenna
yes it is fuel injected.
91-93 octane premium
There are no adjustments on the rear wheels, so no.