Small Block Distributor Recommendation
@Mattax That's pretty interesting. Are all factory Mopar distributors built that way? I see the loop there. I guess it allows it to slip as the smaller spring expands and then the spring with the loop engages to slow down the rate. I hope I'm understanding it right.
Yes - you understand it correctly.
Yes - Pretty much all Chrysler distributors worked that way. That includes the Race units (aka tach drive, no vac advance) but for those, it was super fast in, then super long slow - almost like locked, but better. I drove thousands of miles with one, and as great as it was at the track, I can also say its not the best setup for street.
The primary and secondary curves can be started sooner or later by adjusting the spring perches. That much can be done without disassembly. Changing slope requires changing springs.
Edit: Whatever you decide to do, find out the timing curve used when on the dyno. This is going to to be a good baseline, especially for the mid to high rpm where the dyno was fully loading the engine.
If the shop doesn't have it, go measure it yourself. Use timing tape or a dial back light and measure it from as slow as it will idle until it stops advancing.* If it stops before 3500 rpm, then check a couple points at higher rpm, say 4500 and 5500 rpm.
*With the dial back light, I've come to prefer increasing every 2* from the initial and writing down the rpm that corresponds. When I used a timing tape, I generally measured every 200 or 250 rpm. Do whatever you're comfortable with.