This is a mild cammed 350. I only bring it up because I know this engine made about 14" of vacuum 5 years ago, and today it pulls 9".

Is there a good reason vacuum would lower that much over time?

I just changed the intake gaskets, checked for leaks all around the carb. Blocked off all vacuum accessories... seems like it just doesnt pull in as much air as it used, which is weird, since it seems to run okay.

I'd assume ring wear would be the biggest culprit, but I did a compression test and every cylinder showed 185-195 psi... seems about right.

Im still guessing ring seal just isnt as good ,but I'm kind of surprised it doesnt show up on a compression test at all. I never did a compression test on it when it was fresh built, so who knows what it was then. And I know a compression test is nowhere near as useful as a leakdown test, but i dont have the equipment or patience for that for an engine that is otherwise running fine.

Was just doing some carb tweaks and noticed the vacuum was just a lot lower than it used to be the last time I put the gauge on it... Could be the gauge, but the brakes are pretty firm at times too, so Im guessing it's relatively accurate.

 

Well, First thing to do is confirm that your gauge is accurate. Also, a friend says, funny things about a compression test is, if the rings are starting to go, the excess oil on them can still make a good static seal. So its hard to use that for a base. The only way really is a leak down...

To confirm its not a vacuum leak, there are several tricks, but I use a propane torch, barely open the valve and wave it around suspected areas. you will here the engine rev up when you find it.

Do you have an auxiliary vacuum pump? They need a little oil to live.

 

You know how I check vacuum gauge accuracy? With a vacuum pump.
Make sure your timing is correct too, & make sure it advances when you rev it. Does the vacuum advance get full or ported vacuum? Maybe its frozen.