I also have an 87 IROC 5.7L!!!! Great car. Gave it to my son, minus the nitrous. Got it into the high 13's stock engine, but the standard mods mentioned on the thirdgen site, like deleting the radiator recirc through the throttle body, SLP siamesed runners, adjustable fuel pressure regulator, etc, etc... and into the high twelves with 150 shot of nitrous. Still runs great. Drove it yesterday, got over 21 miles to the gallon with combined city and highway, gets up to 24-25 on the highway exclusively. FAST, unbelievable torque, and handles superb... ur lucky!
Oh, btw, the tranny you have is probably the best year for the 700r4's in the thirdgen run. Strongly suggest you get the TRANSGO performance shift kit for it with the corvette servo for increased line pressures. Our car still "chirps" the rear wheels from first to second.