Opinion:
The Offy manifold is superior to the Edelbrock.
Neither one is going to work well on a Pontiac with the imitation carbs you mentioned, unless you REALLY modify the crap out of them!
Jon.
__________________
"Good carburetion is fuelish hot air". 
"The most expensive carburetor is the wrong one given to you by your neighbor".
If you truly believe that "one size fits all" try walking a mile in your spouse's shoes!
Owner of The Carburetor Shop, LLC (of Missouri).
Current caretaker of the remains of Stromberg Caburetor, and custodian of the existing Carter and Kingston carburetor drawings.
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