On the distributor. Yes, two springs. I would suggest that if you are doing the Pertronix, then do go ahead and get the FBO advance limiting plate. It is an easy way to set the distributor up with the advance that you want. Since you are looking at the Pertronix, you are halfway to having the distributor apart enough to put the plate in anyways. FBO sells the advance plate on e-bay, or you can call them direct...their website is 4 seconds flat.
Regarding spring rates. They might be letting the curve advance too fast, it is something you can look for with the timing light. Ideally there is some but little advance until up to about 1200 rpm at the crank, then it ramps up. If you use the FBO plate, that will limit how high it will go, thus enabling you to set up initial timing at 15 to 18 degrees or thereabouts, while having total advance with no vacuum at about 34’ish. (Remember vacuum is a separate discussion from all these numbers and remains plugged while setting this). FBO provides some nice instructions that will be helpful. (They are good to talk to, and would set up your distributor for you if you wish, they believe strongly in using manifold versus ported vacuum advance, that ends up being a whole, separate, superheated thread).