anybody know where the vacum port is on a 1972 mgb carb or manifold.

I believe the Moss Motors' catalog has a pretty good vacuum diagram. The Bentley repair manual is a good source. Public library may have a repair manual that you can make copies from.

If you have the correct intake manifold there should be a vacuum nipple on the manifold for the distributor vacuum advance capsule. On my 74 it is behind the rear carburetor, item #14 on page 25 of the Moss catalog.

Clifton