Ged117 Thanks for your thoughts on the Super Python, I'm glad it holds up! John has pretty much covered the bases on period-correct derailleur alternatives to the plunger types if that's what you're after for the Sun Wasp (i.e. a Campagnolo Gran Sport) but I would not discourage you from trying one of these out. Thousands upon thousands of them were made and used for rough riding all over Europe and Britain, and three Tour de France riders won between the war's end and 1950 using the same Simplex model I've got here on the Carlton.
If you're taking the time to build up a vintage bicycle with period-correct components, I don't see how avoiding certain ones that were popular and considered reliable at the time is justifiable simply because they don't seem as practical today. Because then you can start to question just about all of the parts - there are bits of rust floating around in the frames, the rotating parts start to get worn or warped, threading gets wearisome to work with as it slowly loses its form, and the brakes can be downright dangerous at times. Bottom line is that I'd be riding a brand new bicycle if that was my take on it, but it's not... 'Tis all part of the experience and it really heightens the senses compared to riding new, perfectly functional machines when you need to factor in the wear and tear and capability of the working parts as you ride along, much like operating vintage automobiles on modern roadways.
John E was the Cyclo derailleur you had labeled for use with a 4-speed freewheel? They were often made specifically to have enough travel to work with 2, 3, or 4 speed chains. The back of the cages say the speeds, and the example on the Super Python says "4 vit. chaine."
Wildwood and to all the others who've complimented the build, I appreciate the feedback and it's encouraging, as I have three or four more to get through! I'm taking a year's hiatus from my graduate school program beginning at the end of the semester in May, and plan to really get ahead on my projects and riding. Cheers!
-Gregory