Use the vacuum pot that came with the Duraspark - I believe it has the required dogleg to best fit the "point plate" that the stator rides on. Some of the pots are adjustable - try sticking a 1/8 hex key down the port and see what you find inside.
While you have it apart - set the two upper rotor shafts on a sheet of paper and draw around the advance slots in the base. Do one on top of the other and you will see the differences in the slot lengths. Just an opinion - I think you will find the 15° slot is too big in the long run. These Y-engines like a good bit of early advance like 10° - 12° is pretty common for the "tuned" cars. If you use the 15° slot and some lighter springs, you'll suddenly find yourself with 40° total and if that's a bit much and she knocks - you'll have to fix it by backing down the initial and that will immediately hurt performance. If you can transfer the length of the 13° slot onto the Duraspark upper shaft (a little file work will do the trick) then you will have a quick choice.
The white wire in the schematic is a "detector" that will cause the system to automatically retard when the solenoid is actuated. So the high initial advance gets out of your way when you want the engine to crank right over.
Steve Metzger Tucson, Arizona