I have a 1948 plymouth special delux we built a 30 over 360 it has a 509 purple shaft in it with a holly 670 street avenger carb. I am wanting to know what I should set my base and total timing at?

15*-16* initial and 36* in full around 2200rpm...

Around 20-24 initial is my guess and the rest mechanical to your total number.

If the car starts and doesn't drag the starter at 20-24, run it. It will idle much better with crisper throttle response than setting closer to TDC.

All of the SB Mopars that I have work on like no more than 32 degrees total timing, unlike the BB and Hemi that likes 34 to 36 degrees, depending on fuel, elevation, spark plug heat range,compression and so on Best bet is try advancing the total timing a degree or two at a time until it starts to ping on hill with light load and throttle around 2000 to 3500 RPM, once it does then back it down 2 degrees