For smaller tracks, I use this combo.
The old Excel Centax clutchbell has fixed 13T/16T pinions. Yes, the 1st gear one way hub and 50T spur is from the Impulse. You need this in order to mesh with old Centax clutchbell pinions. The 2nd speed spur, bell housing and 2 speed clutchshoe (not shown in the picture) from the 705 can still be used as the 705 2nd gear spur will mesh correctly.
With the optional 47T, 22T and 17T pulleys and a 50T/44T spurs, the 13T/16T pinions and 50T/44T combo will give a final drive ratio of 8.22 and 5.87 for the 1st and 2nd gear respectively
