So, in this day and age, there are better ways to control timing than mechanical advance. I have a couple spare MSD 6AL-2 boxes that when used with a locked out distributor you can use to make the timing whatever you want it to be whenever you want it to be. I ran one for about 5 years on my 383 before swapping to EFI couple months ago and it worked great. You can even tie in a MAP sensor to really tie the timing to load as well as RPM.
When I watch the display now of what my Holley EFI ECU is doing to my timing to control my idle and cruise...it blows my mind. I'm not suggesting that you switch to EFI now (but you would love it if you did) but watch this display to see how my ECU makes my stroker idle like a 2016 Camaro.