Adjusting timng with Vacuum Advance

You will need to mechanically adjust the distributor internally. The Mopar Performance distributors have a set screw that locks a stop. Using the tuning kit that is available you take your intial subtract from the 34-36 total and the result is where you want to set the mechincal stop. From the kit you pick the spacer that is the closest to what you want and put in the advance slot and adjust the stop to the spacer. MAllory distributors work the same (the MP uses a Mallory mechanism). Accel distributors have graduations that you adst the stop to and MSD use different size bushings.

If you have a stock distributor then you will need to take it apart and weld or epoxy the slots and through trial and error file them to the correct length.

There are spring kits that allow you to adjust the rate at which the mechanical timing comes in. Most kits will have charts that you pick the curve you want and from that it tells you what springs to use.

Lots of folks will just set the total timing a 2500+ rpm and call it a day. This leaves a lot of tuning and improved driveability on the table and is a very innaccurate way to set timing, it works OK for a race only motor but not for a street driven vehicle.

You need to find the initial the engine wants and you do that with a vacuum gauge by increasing the timing until you find max mainfold vacuum. Then adjust the mecahnical advance mechanism to give you what the heads want. Open chamber small block mopar heads like 34-36, more modern heads like magnums and aftermarket ones will like a little less. This is something that can only be dialed in with a dyno or many drag strip runs. The vacuum is then set up as I previously mentioned.