Timing curve for my big-cam 451?

When I first got my dart, it had two Mr Gasket springs in it. It would crank at the initial timing and then run at max advance at idle.

You could probably get away with the same thing on your setup.

Otherwise, I'd try to pull in more with the vac advance at idle and then still lighten the springs. However, that can still cause an erratic idle, especially since your vac signal is likely to be messy at idle with that big cam.

Another option would be to use a programable ignition that you can custom map. But that's not real cheap either.

I'd try option one above. Between the low cranking compression and the small amount of advance, having it effectively locked out with mechanical timing retard would probably work well.