One could cut a spur gear with 40 teeth for that 40:1 ratio, but I doubt it makes any difference in the universal world of mathematics. Multiples with more prime factors will give more flexibility. 21:1 is 7*3*3, which does not have a 2*2=4 factor. That will limit you for sure, but 12:1 or 20:1 or 24:1 sure has a lot of workable indexing options. Any ratio that goes into 360 evenly (1, 5, 30, 40, 180, whatever) is a good candidate for a simple degree wheel RT, without need for indexing plates.

I think the backlash compensation scheme on my Kamakura RT would work well against that worm gear. The gear would be bored and shafted on one side to work your handwheel. Against the opposite side, a simple plunger and spring would force the worm gear toward the handwheel side to squeeze the backlash out of the gear pair. You'd have to look at some pics of various RTs to make sense of what I said, but I think those parts are suitable for it if the OP were to pursue the idea further.