I have had a question about nitrous systems, this might be the moment to get it answered. Can you drive around the hood for months with the bottle open just waiting for the opprtunity to use it, and when you finally went WOT the gas would be there for you? I ask because I heard all the systems leaked and if you needed a shot you have to go out to the trunk and open the bottle and then close it when you're done. <bummer>
Don't waste you time with the NO2 system, Do the basic hot rod / Simple tricks. Leave the Nitro's for the race cars.
Buget Things to do.
Cam, Lifters and Timing chain + a good set of springs, Comp Cams Extreme Energy series has some nice street grind that will work well in your motor + a few other makes like Lunati, Crane Ect. Keep the intake duration @ .050 no more than about 218-220 and keep it below .525 lift.
Recurve 0r new distributor (MSD Stuff is nice) + wires and correct spark plugs.
Headers and good Dual Exhaust. Use smaller tube street headers and 2 1/2" Exhaust Pipes.
Convertor / Shift kit. (2000-2500 stall)
Gears (3.50 and up, But no more than 4.10's depending on how tall of tires your runnning)
Good Intake Choice ia a Edlebrock Performer RPM / 650-750cfm carb
Your heads will work fine and your 9.3:1 Compression is fine and makes the car pump gas friendly.
Everything assumes your motor is in good running condition and is not worn out. If its worn out and needs a rebuild then consider making a 390 out of it and doing some head work.
Yes Edlebrock Alunimum heads can make a big differance, But they cost around $1400 and get away from the budget theme.
The above mentioned modifications will get you well past you goal of 50 more hp and will wake up your car.