i have a black 1986 z28 with a holley 650cfu on a 305 engine also have a red 1990 iroc with a 305 tpi both are parts cars and i dont know which one is more worth keeping the z28 has a better body but the iroc has the engine and i like the newer look of the iroc which one is easier to upgrade horspower and torque wise?.... cant decide here -__-

 

The 1990 is quite a bit superior mechanically.
The 1990 has a nice 730 ECM for running a SD TPI, and the engine is a roller block with roller cam/lifters.
As far as modifying, that is up to you what you feel more comfortable with.
TPI tuning requires some electronics and is much more involved, and will cost more. Most people prefer the results though.
The 1990 parts will fetch much more money in sale.

If you need it to stay very cheap and relatively easy, then stick with your 1986 carb engine.