paintinx - It sounds like you want to dive into the fascinating world of Qjet tuning and optimization. Your carb number is correct for a 78/79 truck and fortunately has the hot air choke which is easily converted to an electric version. The primary circuit of a Quadrajet is controlled by more than just the jet size. The primary metering rods and the power piston spring are a huge part of the equation, and merely changing jet sizes isn't always done like it is with Holley or Edelbrock.
I would strongly suggest that you visit
Cliff Ruggle's site and buy his book. I've been messing with Qjets for years but didn't achieve real success until I followed his instructions and used his kits. Perhaps the best service he offers is a complete tune kit - give him your engine specs, and he'll sell you the correct jet, metering rod, idle tube and power piston spring for your application. He also runs an excellent forum on the site which provides excellent help and advice. I can state from personal experience that once a Qjet has been properly dialed in, it is difficult to distinguish from a comparable rig with aftermarket throttle-body fuel injection.