Streetmaster 318???

Typical and proven performance hop-ups to a 318 include dual exhaust, 4-bbl. carb, and cam/lifters/valvesprings for starters. I'd personally recommend first getting dual exhaust off the stock manifolds (crossover does help too but it's arguable at this level of HP). Then swap on a good dual-plane intake such as the Edelbrock Performer and a 4-bbl. carb such as your 1405 which is a 500 cfm model. Then if you want to go further I'd recommend first getting some good replacement cylinder heads (such as the #302 casting heads from the late 80's) because the ones on your engine are pretty awful flow-wise. Combine that with a good cam (Lunati Voodoo series is great, I have one in my Duster) and some higher-compression pistons (if you want to go that far) and you'll have a screamer. Really with classic American performance you can go as far with the engine as you want; you could build a 400 HP 318 for not too much money, but then again a 360 is an easier choice. I have a 1970 Duster with a 318 and so far it has an iron 4-bbl. intake off a 360, a Carter Thermo-Quad carb, and Lunati Voodoo 256/262 cam with Comp 901 valvesprings. It's still kind of sluggish though because it still has the tiny single exhaust and stock torque converter with 2.76:1 rear end gears (plus my secondaries aren't working right which definitely doesn't help).