Every 235 I've seen has a manifold vacuum port about 2" below the carb mounting flange for a windshield wiper hose. If there's not one there, a quick drill and tap job in one of the manifold runners going to the front or rear is an easy fix. A 1/8" NPT thread is plenty to install a hose nipple for a vacuum gauge.
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!