Steve,

The vacuum port for the fuel pressure regulator on my 91 is just below
the power brake booster on the engine's driver side of the intake manifold.

I believe that is the only true vacuum port available. I inserted a tee
connector to the hose for the vacuum gauge.

My engine reads 13" now, it has run as low as 10.5".  I'd say 11- 13 is
about it for a boxer at idle.

Sincerely,

Mark Keller
91 Carat
Cowichan Bay, BC