missing power
Well, there is a multitude of things that might be amiss with your 302. First off, sounds like you have a nice combo of parts. You never mentioned how much power it has and how much you expected. You also never mentioned your cam or how its timing was set when it was installed. Anyway, that aside and assuming you have a problem.
Check your vacuum reading, this will check for intake manifold or carb leaks. Thats always a possibilty on a newly bulit engine. (all those bolts need to be tightened just the right amount and in the right order) An old trick if you suspect a leak is to listen for leaks using a piece of hose up to your ear and pass the other end around the manifold & carb joins, you will hear a leak as a distinct sucking hiss.
Carb jetting: are you using the right jets? Carb Float level set ok? Fuel filter not blocked?
Oh yeah, here is a simple, common but often over looked fault, check that the throttle pedal fully opens the butterflies of the carb, sounds dumb but if it doesnt then theres all your lost power. Also while you're there, another often overlooked problem, make sure the choke is coming off fully (auto when the car is warm, manual when the cable is pushed in)
Then there is your timing, check the static timing, and the advance timing at revs. You may need a rebuilt distributer.
I assume you got nice new plugs, dizzy cap & leads, did you set the plug gap correctly? also, if you dont have electronic ignition then make sure the points breaker gap is set right.
Hope that helps some.
cheers n beers. Mick