New to Tuning, How to read vacuum

Put that vacuum gauge back into the toolbox, it will just make your life miserable.
That gauge is a pretty good diagnostic tool.but
IMO it is useless as a tuning tool.
While you are throwing things away, I highly recommend to upgrade from points as soon as you are financially able. Not that there is anything wrong with points other than they are just one more thing to complicate your life.
As to your rich-running; Ima thinking one or more of; the PV diaphragm is blown, the choke is on,the accelerator pump circuit is siphoning, or the float-level is too high/unstable.
As to the tip-in stutter; Ima thinking the transfer slot exposure under the primary throttle valves is too short.
A stutter/hesitation not on tip in is likely a lazy accelerator pump.
If your engine has been running rich for all 500 miles then, likely the ignition system will not be able to clean up the plugs. If they are black and sooty,throw 'em away, and while the plugs are out, do a compression test.
Ok, with the baseline now prepared;

The first thing you need to do right now is to;
Install a NEW PCV.
Start with fresh from the pump, whatever gas you will be using, and want to tune for. Your engine should be fine with 87gas. Higher octane gas will not make any more power ...... unless your engine detonates on 87.
Remove your squirter nozzle and prove the checkvalve is in there.
Then,set your minimum coolant temp to as high as your location will comfortably allow. This temperature must be stable at all times. If it is not, then fix it! You will have no tuning success if your engine temp is dancing around between 180 and 220, so fix it. I run mine at a minimum 205*F, and it maxs at 207*F,lol.Get this done.
Then remove the carb, flip it upside down, and set your transfer slot exposure underneath the primary throttle blades to between square to a hair taller than wide. Then make sure your secondary blades are closed up tight but not sticking. Shine a light up from the other side and make sure they are absolutely both closed. Next,reset your mixture screws to 1/2 turn from lightly seated, and, and, and, after this leave all those settings alone.
Finally set your accelerator pump preload. then
Reinstall the carb, prime it and start the engine. Now verify the float levels are correct. This is critical for your combo; it will not tolerate a setting very far from the Holley Spec.And make sure the choke blade is vertical and stays there.
Ok, now;
To set your idle speed;
you will back up the timing.
Without a tach; set the park brake and put it into gear; then just back up the timing, back it up,back it up, don't even look at the timing light, just back it up until the engine wants to stall; then put a little advance back in. Forget the light/ forget the vacuum gauge.
With the engine idling, stick your index fingers on the boosters, and make sure the idlespeed does not change. Then stick a shoprag into the secondary opening and make sure the idle speed changes not or changes very little.
Now, put it into Neutral and and back into gear a few times, noting how badly it clangs into gear and how much higher the neutral rpm seems to be. If you think you can tolerate a lil more jump, pull in just a lil more timing; do not adjust the curb-idle speed screw.
DO NOT TOUCH the curb-idle screw.
Ok having fixed the N-D jump and the high idle, take it for a roadtest. You are only checking the low-rpm response, do not change the curb-idle screw.
Watch for a tip-in sag, or hesitation, a flat-spot or an outright bog.
You should have none of those.
But if you do get a tip-in hesitation, NOW, you can screw in the curb-idle speed screw one half turn, and repeat the roadtest. You can do this a total of two or maybe three times, to solve a tip-in hesitation, which is from curb idle to just off, in gear and leaving a stopsign. If it does not go away with a turn and a half, something is wrong, put it back 1 turn, and report back.

Then; Ima thinking; 66/72 jets are gonna be too lean/time will tell.
After you solve your rich problem, you are gonna need to swap out whatever PV is in there , for a 10.5, and
probably upjet to at least 68/74.You may as well order those now. Put the 10.5 in with the 66s and roadtest that.

That's all for now.