This should really be in the turbo and nitrous section and you should really use proper grammar here, or people will ignore you. It's been a few years since I ran a 420a, but I'm pretty sure the upper limit on the stock bottom end is close to or under 300 at the crank. You're going to have a hard time getting that at the wheels on a stock bottom end and keeping an engine. If you're serious about making power on that platform, a built bottom end is in your future. If it were me, I'd be more worried about getting that than about nitrous.

You're on the right track with megasquirt. I don't remember there being too many other serious options for a 420a unless something changed after I moved on. I didn't see anything about injectors in your post, and the stock ones aren't going to flow anywhere near enough for 300hp, especially on e85. You're going to need a high flow filter and the lines to connect it. You're going to need an AFPR. Basically, the pump is step 1 of about 5 for your fuel setup.

Read through the how to turbo your car threads in the tech articles section. Yes, I know you don't want to turbo your car, but the fuel lectures will help you figure out how to calculate the size injectors and pump you actually need. Remember to compensate for the increased fuel consumption for e85. I forget if it's a 20% or 30% increase over 93, but either way it's more pump, more injectors, and/or more line pressure. E85 effects what kind of filter element you can run as well.