If you are on a budget, a used set of EVO8/9 injectors for $100 will give you more than enough fuel for 300HP. But, as others have said, you will also need a fuelpump and MAS upgrade to go with it. If you stick with an EVO8/9 fuelpump you can probably get away without an AFPR, and just lean the idle out with the AFC if you overrun the stock FPR.
Have you checked to see if you have an EPROM ECU?
89-94 EPROM Check
You *can* compensate for larger injectors and a 2G MAS with the AFC, but its going to add extra timing advance, which will cause knock issues. Also, the factory timing maps stop at <15psi, so you are going to have the same timing at 20psi as the factory only intended for 15psi. That's the main reason that a chip is the better solution.
With that FMIC, bigger exhaust, and enough fuel, I don't see why you shouldn't be able to run 20+ psi, as much as your octane will allow. I just had one customer with that setup and an EVO3 16G do 358 awhp @ 23psi with nothing to tune with except my chip.
keydiver