Is there any real advantage to updating my 305 stock distributor to an HEI distributor?

If so, what kind should I look for? Vacuum advance or mechanical?

The stock distributor is HEI.

So an upgrade to say MSD or Accel is really not needed?

My preference is GM parts. I use JY GM ignition modules over new 3rd party modules. Along with ignition coils. The pick up coil I'll use an aftermarket piece.

Although getting tougher to find, I still pull entire stock GM distributors from the JY when in decent condition.

RBob.

HEI was GM's trade name for their electronic ignition distributor systems. Every distributor in every GM car from 1975 onward until was HEI until conventional distributors were replaced by things like Optispark and DIS.

Upgrading ignition components doesn't result in any noticeable performance increase in street cars.

so my stock dizzy should work fine for tfs 300300003 heads hedman full length headers 650 demon carb 268xfi h13 cam, rpm airgap..?

YES...IF (big IF) it's in good condition.

The DESIGN of the OEM parts is fine. They do wear, and the magnets in the pickup coil can wear out.

The small-cap HEI on my K1500 failed over time (somewhere beyond 200,000 miles) due to the magnets on the mainshaft cracking.

If the distributor you have is in good condition, you will gain NOTHING by upgrading to aftermarket parts. Depending on what you'd choose, you might sacrifice reliability in the process. The Chinese replacement distributors are notorious for problems.