Carb keeps catching on fire!

[Syco67]

I am getting ready to help my friend swap a 350 from a 73 1/2 ton truck in to a 78 1/2 ton truck, but we are worried about the condition of the engine, it was running fine, then my friend sold it to his neighbor, then bought it back a few months later. he had gotten rid of the edelbrock carb (traded it for drugs) and put on a jimmy-rigged Q-jet from an 80's model camaro, every time we try to start it, it will start to run and then begin popping and shooting fire out the top of the carb. None of the valves have dropped, and the engine doesn't make any other noises. This guy had a habit of starting the engine cold and flooring it until it warmed up. We are hoping the carb is the problem, but don't have another one to swap and check. What else could we check.
TIA