On a stock HEI distributor the meacnical advance is limited by the advance weights topping out. The problem with this is that the timing can and will creap up at higher rpms instead of truely toping out at around 3000 rpm.
This is why I recomend what I recomend. Physically limit the travel as shown in my pics or use a ( custom) 10° advance limit bushing on the pin in the slot.
Most stock HEI`s have no bushing on the pin and depend on the weights contacting the center piece under the rotor to stop the advance.
You want and need more than 14deg inital at idle. Install the screw to limit the travel so the initial can be around 24+/- deg at idle and the max advance is 34-36deg and does not creep up at hi rpm.
This is the easy way to get the desire curve and stop limit.
Use two medium tension springs or 1 light and 1 medium
Light springs result in inconsistant mechanical advance operation.
22-26deg base at idle +10 to 12 deg mechanical advance =`s 34 to 36deg at max advance. (approx 3000 rpm)
Fix the distributor. Its not rocket science..and 14 inital is not enough. Its like nobody reads my many many posts on this thou.
(if you were running a automatic trans with high stall converter you could simply just lock out the mechanical advance) but you`re not.
Fix the vacuum advance system too.