Vacuum reservoir for power brakes

With 14-15" of vacuum you shouldn't need a reservoir for the brakes, that should be plenty of vacuum if everything is working properly.

I'd swap to manual brakes long before I added a reservoir. I swap all my cars to manual brakes anyway, I prefer the pedal feel and brake control with a 15/16" master cylinder to any of the vacuum boosted set ups out there.

If you still want to add the vacuum reservoir, there shouldn't be any reason you couldn't add the reservoir off of the intake connector and leave the original alone for the heater control. Shouldn't hurt anything.