I am not into performance so this subject is not all that familiar to me but I think this is the basic concept:
Installing a center plate with the 375 cam contours, a set of 41 fly-weights (and often a set of lighter fly-weight return springs) is actually what is commonly referred to as "re-curving" a distributor. A recurved distributor is intended to more quickly advance the timing using the centrifugal advance mechanism. This allows for somewhat quicker acceleration during periods of heavy load change. It will not increase low end torque.
A 375 center plate has the cams cut in such a way that it cranks the timing up (advances it) faster during an initial heavy load application - i.e. - WOT.
When you first start to accelerate, for the first few seconds, the timing is controlled only by the mechanical advance part of the distributor. That includes the center plate, fly weights and springs.
The vacuum advance acuating diaphram is attached by linkage to the center plate, but it is out of the loop during conditions of WOT. It does not come into the picture until the throttle is no longer wide open. At some point sufficient vacuum is developed in the intake system to stroke the diaphram and linkage of the vacuum advance system.
Then, until the throttle opens wide again and vacuum drops, the actuating linkage of the vacuum advance overrides the mechanical advance and continues to regulate degree of spark advance.
As long as intake manifold vacuum remains high enough, the vac advance stays in control. The function of vacuum advance is primarily one of fuel economy.