2.89s were never a gear option for Thirdgens, hes most likely running 2.73s through a 10 bolt which really suck monkey penis. Gear swaps are a very common upgrade in the Thirdgen world. Going from 2.73s to 3.43s or 3.73s make a world of a difference in thirdgens.
SLP Shortys were $180, Gears was a 9 bolt swap $300, A Lt1 cam can be found anywhere for cheap $50, Porting was DIY. I was about a grand into the car after it was all said and done, meaning gaskets, fluids included. I didnt spend more or wish to go further since there is no point with a 305.So wait... You did headers, cat back, gears, a cam, and a tune for the same price as a 3.4 setup???? Not sure I believe that...
Things are really inexpensive for Thirdgens.
My point in this is yes a 305 L03 (TBI) or basically a plain jane RS Camaro or Firebird will get beat by a GTP pretty bad since their high 15 1/4 cars, but 305 LB9 (TPI) G98 are more of a challange and like I keep repeating myself a 305 LB9/T5/3.23 Stock setup with a good driver would be pretty equal. All of which are 305s.
Now 350s are a different story. My 86 Firebird Sleeper had this under the hood:
97 LT1 Stock Shortblock
Ported 643 Heads
Ported LT1 Intake W/ 58mm SR TB
CC503
Hooker 1 5/8 Shorties W/ EGR Delete (Hooker 1 3/4 Longtubes Scrapped really bad)
GMMG Catback
4l60e W/ Yank SS3600
89 9 Bolt W/ 3.77s
Lt1pcmtuning Tuned
Suspension was Koni Yellows all around with Founders Performance & Spohn Goodies.
You seriously do not want to know how much I was into this setup, and I know for sure as much as I love my GTP, it wont ever bring a smile to my face as my old 86 did.