Way back when I had my first Volvo, a 1973 164E/Automatic (bought new), I was putting a lot of miles on it commuting and it felt like it needed a tune-up (including adjusting the points) every six months or so. Fed up with having to adjust mechanical points each time ...
[it wasn't as easy as a contemporary GM's Delco, which could be adjusted (a hex insert through a metal "window") with a dwell meter while the engine was running (giving a more reliable reading); the Volvo was a "trial and error", even with a good feeler gauge.]
.... and envying the electronic distributor introduced on the '75 model, I converted my '73's distributor to electronic with the Allison aftermarket kit -- it had a chopper wheel very similar to yours, except that it was metal instead of (what looks, in the photograph, like) plastic.

But if you need your distributor (you've specified 1973 in the subject) to be original, as I recall the Allison's installation didn't require any irreversible modification -- you should be able to just remove the sensor block and reinstall the points, condensor, etc., just like OEM.

Good luck.