Woah.... Here it goes.

If its TBI injected, then its a 305. In 92, you could have got a 305 TBI (RS), 305 TPI Z/28 (tuned port injection) and a 350 TPI Z/28. Another way to tell the car apart is if you had a 350 TPI Z/28, there was NO T-top option. Only the 305 TPI Zs could get T-tops. You could also look at the VINs. The 6th or 7th (dont remember off hand) will be a "F" for 305 or "8" for a 350.

Now, as far as the motor. If you are strapped for cash, I would honestly save for a L98 350 swap. You can pick them up for cheap. I would also save for a different intake setup, like the miniram from TPiS. The stock TPI plenum sucks ass. Its torquey (is that a word?) off the line, but it cant breath aboove ~4000 RPMS. It just falls on its face. After the swap, a small cam, new intake and the normal stuff like bolt ons, headers, good catback and such should put you over 300 HP reliably.

Have you ever had the car on the dyno? I know the 305 TBI motors might put out like 170 HP.