So, you're sayin' you have only one manifold vaccuum port? The one in the pic? There's no threaded plugs anywhere else on the intake? How 'bout just inboard of the carb? Don't know much about 235's or 261's but, I'd think even if the motor was original and without PCV, you'd at least have two vaccuum ports. One for wipers and one for a brake booster if vehicle so equipped (plugged if not).
Did the fuel pumps on old Chevy motors ever supply vaccuum? I think the wipers on my Pontiac are powered from a vaccuum port at the fuel pump.
