One of the stickies is chock full of vacuum diagrams.

The bowden cable affect shift timing. If the shifts occur when you expect, don't touch the cable.

Vacuum affects shift firmness - more vacuum means softer shifts. The VCV mimics manifold vacuum in a gasser. The VCV linked to the throttle linkage to the IP varies vacuum from what the pump puts out, about 20" Hg, to nothing under WOT. You can test this with a MityVac, vacuum gauge and your hand on the throttle linkage. Engine running or not, your choice

Sixto
87 300D