[68 P.O.S.]

34 isn’t bad if you have no pinging. Play with it a bit, but the sweet spot for Vortecs is supposed to be about 32 degrees. Yes, your timing light should match either way you do it, so something’s not right. Maybe the distributor advance springs are too strong and aren’t allowing full advance at 3K RPM. If they are the original springs, those things are way too strong and don’t allow full advance until about redline. You’ll have better luck pulling the springs out, then re-timing it and see if there’s still an issue. Have you verified TDC with a piston stop to make sure the balancer isn’t slipping? Since you replaced the spark plugs, did you gap them to 0.045 for HEI? Did you did replace the plug wires as well?

I just re-read this thread and in your first post, your description of having to blip the throttle to bring the rpms down just reminded me I had a problem like that once. I would start the truck and it would idle at 750 as normal, then after going for a drive and parking, the idle rpms would be at 1000. Would have to blip the throttle to bring it back down. What fixed mine was pulling the carb off and squaring the transition slots. Also, adding a CDI box like a MSD will really smooth out your idle too.