A BIG vacuum reservoir with a one-way check valve will make a huge difference in the shifting speed. I have used empty Freon canisters and occasionally a recycled Propane gas grill tank for upgrading vacuum systems on bigger trucks where there's lots of room to hang a big tank off the frame. It also improves the reserve capacity of the brake booster in case of an engine stall.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!