Hello Bryan,
there is no vacuum advance when you are accelerating, no matter where you are on the rev band. If you disconnect it with the original set up then it won't run as well at cruise because the mixture is a bit too weak. Adjust the carburettor to compensate then it will run well. Likewise if you put a different carburettor without a connection then you need to set the mixture up for all conditions.
Don't be misled in thinking that a lot of advance is necessary for power, particularly if running at above the 'ideal' ratio of 14:1 petrol to air. Power requires a more than ideal quantity of petrol to air, and that needs less advance. Too much causes detonation, modern engines have detectors and the computer adjusts the timing automatically. Older cars without knock sensors have no such protection, and if it starts detonating, you won't hear or feel it, until the engine is damaged.
What size is a big block Chevvy? Basically I was saying that size for size on normal road cars the American engine is not as powerful, i.e. Horse power per cubic inch.
Alec