Sounds like you really want to try 80s electronic controls on your GMC. FYI the Olds V8 continued in 307 cu in displacement through 1990 in some full size GM cars. These later years all have electronic quadrajets and HEI. I don't know if they had knock sensor control.
For what it is worth I'd stick with the OE quadrajet. They are incredibly tunable and if you are familiar with other carbs you can learn quadrajets as there are a few good books devoted to the subject such Doug Roe's book. The later years (76-78) have adjustable part throttle (APT) metering. Between primary jetting, primary rods (the GMCs are a special triple taper), secondary rods, primary power piston springs and the APT the Q-jet can be dialed in quite satisfactorily. It just takes a linear lambda gauge, an assortment of jets and rods and careful note taking. The only downside relative to fuel injection is the lack of altitude compensation. I may get some argument over this last point, but there are many here who will agree that the q-jet is actually pretty darn good in terms of performance and economy.