Amdscooter,
Look up duraspark recurving instructions on the internet. You'll find a distributor bible I have learned to live by. I weld up my mechanical advance slots on all my distributors to give me 34-36 total degrees.
I'm using the Mr. Gasket distributor springs on my 410 build but I can't tell you how long they'll stay in there. I found I couldn't run them on my 406 with C6 transmission and run a vacuum advance too. For me to be able to get the idle down to a permissible rpm to keep the transmission from being torn out of the car when shifting from Park-Reverse-Drive I had to go to a Duraspark that allowed me to set the initial at 17 degrees and still start it after it had warmed up. The Duraspark retards the timing 6 degrees on startup. My max total is set to 34 degrees but I think it'd take a little more total.
From my observation I've found the Mr. Gasket springs are for all out acceration. Having springs that give you maximum mechanical advance at 2100 rpm plays hell when a 10 degree vacuum advance kicks in at the same time. On my 406 I got full advance at 2100 rpm, not 2500. When you start out with your foot on the floor you don't have to worry about the vacuum advance working. Besides that, I can't imagine making a stock distributor work with a bigger cam at slow speeds and cruising.
My advice to you if you are running the Mr. Gasket springs is to limit your max rpm by welding up the mechanical slots to get the 20 or so mechanical and 14 or so initial so you don't have to idle at 1000 rpm to keep your engine running.
There are advantages to running a $500 aftermarket distributor system on your car. You don't have to learn anything and just have to follow the wiring schematic. Just kidding, they have rev-limiters, little LED lites that flash, you have better control over timing at 6500-7000 shifts and they can produce another 10,000 volts of energy that you don't really need with their super-duper coils you have to buy to go along with the modules. LOL Good luck.
