Lots of needed information to really make a suggestion, so will try the "shotgun" approach.
First, smog emission no longer need play a part in your decision (assuming you live in the USA). Federal smog emission requirements took effect with the 1968 model year. California smog emissions originally took effect with the 1966 model year; however California law SB42 rolled the more-stringent California requirements back to the Federal level for 1974 and older. Since the Federal level for 1966 wasn't, then smog testing need no longer be a problem (unless you have a local retrofit law).
Not familiar with the mentioned manifold, but use a carburetor that is matched for the manifold. If you want a spread-bore carb, use a spread-bore manifold. If you wish to use a square-bore carb, use a square-bore manifold. Don't use a adapter to adapt square to spread or vice versa.
The spread-bore design works extremely well on the street.
Q-Jets were designed for a specific application (not aftermarket). As such, migration of a Q-Jet from the original application may work well, may work OK, may work poorly. While all pre-1971 Q-Jets were 750 CFM, this is a WOT (wide-open throttle) measurement. The CFM delivered at less than WOT depends on the original calibrations.
We like to categorize engines as "torquers" or "screamers". Chevy small blocks are screamers (high RPM). Pontiacs are torquers (high torque, but not so high RPM). Mixing a torquer carburetor with a screamer engine, or vice versa; is normally going to require some internal modifications.
Biggest current drawback to the Q-Jet is tuning parts availability.
The book you should procure if you plan to do any modification of a Q-Jet (or any other Rochester) is "Rochester Carburetors" by Doug Roe and Bill Fisher, published by HP Books.
Personal suggestion for a Chevy 4x4 with a small block is a Carter TQ part number 9800. This TQ is an 800 (200 primary, variable to 600 secondary). The 750 TQ is 150 primary and variable 600 secondary. While you won't probably ever need 800 (or even 750), the truck really likes the extra 50 on the primary. Again, this is a spread-bore design, and requires the use of a spread-bore manifold.
Jon.
