If you put a 350 in it you will get 180 HP and 300 lb.ft. of torque. If you put a 350 from a 91-93 9C1, you get 205 HP. Used ones are about $350 at the pic-n-pull junk yards. They bolt in, but you need the computer for about another $50. The 9C1 has a similar cam to the LT1. Larger 9C1 Y pipe, and exhaust system (you can get the cam, injectors, computer, and exhaust for your 350 to make it a 9C1 350).
Put an extra gasket under the injector holder on the TBI to open the intake path.
3.23 gears will make it feel like it has more power, and will not affect your gas mileage. The gears in the VSS will have to be changed to match the gear ratio/tire size.
If you are going to install a cold air intake, move the charcoal canister under the wheelhouse with the bracket from a 94-96 (found on the opposite side).
The dual fans from a 93 FW are a perfect fit, and you only have to figure out how to turn them on. Temp sensor with switch, and AC clutch...have them run by relays. Electric fans will give you about 5 HP.
From here on, you are going to have to get the computer chip burned.
You can use the larger TBI from a 454, and the injectors from a 9C1. You will have to bore the intake out so there is no lip where the TB and the manifold meet. You also have to get the larger gasket set, or open the holes on a set for the smaller TBI. The connector for the cruise control is larger on the larger TBI, and you will have to ream the end of the cable as well as a larger clip. Adjustable fuel pressure regulator, and fuel lines from a LO3/5 equipped 91, 92 or 93 FW with Schrader valve for a fuel pressure gauge installation.
Cam of your choice, springs, rockers, etc.
Headers (about 20 HP), duals, and modified trans crossmember/redesigned crossmember for duals.
Reasonable expense for another uprade is a 350/5.7 Vortec engine from a later truck with its wiring harness, computer, and possibly the transmission. You will have some wiring adaptation, and maybe the FEAD, or use the one from the LO3 if the bolt holes match. You might need a stronger fuel pump, and a reprogram for the computer. Cam, headers, valve springs, duals, trans crossmember mod, are all doable with a Vortec engine as well. The engine should be the same price as a 9C1 at a pic-n-pull yard, just a little more work, because of the different wiring. You can make more HP with less money with a Vortec than you can with an LO3/5.
Next step up is the LS series engines and matching trans.
If you do it yourself, the mods are relatively inexpensive. If you have someone do it for you, it can get expensive fast.
1991 OCC 461 (.030 over 454) BBC, 3.23 posi, flash to pass, drop spindles & springs, Impala rims, Hydroboost, Recaros, MOMO/wood SW w/QR, custom wood shift knob, Pioneer DEH P77DH
1992 OCC now with 5.7 tbi, DEH P77DH
For a parts list, check https://www.impalassforum.com/vBulle...ion-parts.html