Thought of another challenge someone might have info on. I notice that the vacuum wipers increase/decrease in speed relative to engine vacuum. Would a vacuum boost/ limiter of some kind help to stabilize this? Any ideas?

I used to have an old Mercedes with power door locks. They worked off vacuum. Vacuum chamber was a plastic egg-carton looking affair that hung in the trunk under rear deck. It was connected to carb (vacuum source) and lock mechanisms were connected to it. Various check valves in lines assured vacuum was held until needed. I bet if you hooked some kind of vacuum tank like that to wipers they would work pretty steady (for awhile at least). Think of the luxury--they could even work for a bit with the engine off!!!

to assist power brakes when using a radical cam. It has the check valve built in and cost less than 40 bucks. Should be plenty of reserve vacuum for wipers.