It's an easy swap. With TBI the in tank pump pressure should only be around 15 psi, just use a regulator to get it down to 7psi. Easy to do since you already have a return line. Depending on year, application, or if you have a Goodwrench replacement engine you may have provisions for a mechanical fuel pump. My 89 GMC had provisions but my 92 Chevy didn't. Swap the intake to something like an Edelbrock 2104 spreadbore. Use the correct TV cable bracket. Then use your HEI distributor and you're good to go. Unless I'm mistaken the ECM can be retained to control the transmission if needed and aftermarket switches are available for TC lockup. My only experiences with this type swap were with 5 speed manual and TH 400 transmissions. I only disconnected/deleted wiring that was directly related to parts I changed or removed, and the ECM was left in place. I just learn to ignore the CEL. HVAC systems don't operate through the ECM. Though you may run into dieseling issues with carburetor and using air conditioning. You may run into issue with the catalytic converter having a short useful life span if you choose to keep it.
The real power killer on these engines are the heads. In my opinion a set of Vortec heads and intake are a huge improvement with the factory TBI.
This swap is popular because the 2 barrel TBI just can't handle over 300 hp. The stock throttle body is rated at about 480 CFM. That's too low for a 350ci engine. Even a 670 CFM 2 barrel throttle body is too small for a healthy 350ci engine. Just check out the Holley Pro-Jection system, 670 CFM and still only good up to 275 hp.
When I had my 92 Chevy K2500 with 5.7 and 5 speed it sucked to drive on the interstate pulling a 5000 pound trailer. If it had a tow package with better gearing it would have been better but as it was I either needed to spend a lot of money to re gear both axels, replace the 140,000 mile engine or put a better induction system on the engine I had. A used Q jet and a cheap intake of unknown make and the problem was mostly solved.
As far as horsepower is concerned this swap is THE best bang for the buck. It is detrimental to emissions though. As far as MPG the loss you see there is comparable to the gain in power.
