Well, did this right before the torrential rain arrived in PA. Haven't had a long test, but so far it feels good.
Made my own timing tape. Set initial timing to 10. If I set it to 8 or 12, I get slight dieseling. Amazing how small of an adjustment makes a difference.
I found a way to see the timing marker with the gun, so we were in business. What was interesting was my vacuum/hand timing had set it at about 20 degrees initial timing (maybe 18). That's where the engine "sounded" happiest. At full throttle, timing was around 40 with some lovely little pings at high torque load.
By setting initial timing to 10 deg, I noticed the engine does sound like its working harder but the engine is more responsive, less vibration, and sets the vacuum timing to hit right at 32 degrees with higher rpm.
So, I went to the Google machine and low and behold, every article I could find about a vortec/SBC 350 suggests 10 degrees initial and 32 to 36 degrees at higher RPM.
I've certainly learned a lot by this process and hoping I solved the issue. Have to wait for the rain to stop so I can do a longer test drive.