Roger,
My Jr. Varsity wears the UnionFrondenberg, as you mentioned. And I would be 99% sure that is how it came from the factory.
I worked in 3 different Schwinn shops from 1971 -1977 (jr high-part of college), but can not answer your question (was a long time ago). However, I do remember on occasion bikes coming from the factory with parts not stamped "Schwinn Approved" (had the manufacturers name instead) cables that needed to be cut down (for another model) probably due to shortages or a supplier mistake and some slight differences of some products (i.e. handle bar tape that was a shade off, not as transparent, etc) probably a different supplier. But this was more common in the earlier 70's during the huge shortage years. I remember telling people we have no Varsities (as an example) for sell, this is a floor model, not for sale, only for people to see, to place an order. You can get one in about 6-8 weeks (if you are lucky). Repair shop backed up, 6 weeks wait for a repair (unless it was a flat tire or a 30 day checkup). It was crazy!!.
I bet we sold 50 adult Varsities to every Jr. Varsity. So while I assembled/repaired a ton of Varsities, only a handful of Jr. Varsities and do not recall if the pedal were different, unfortunately. I do remember the Jr had narrower handlebars and I believe shorter crank arms and maybe a shorter kickstand. Otherwise, all the same parts as the adult.
From a manufacturing standpoint, if both frames are made at the same location (I am not sure) and boxed at the same location, why would you try to keep two interchangeable parts separate? Would just add more work and possible delays if a shortage of one of the manufacture's part. But who knows.
When trying to figure it out, make sure to compare same year (maybe even same month manufactured) adult Varsity to Jr Varsity. Both models may have changed, if Schwinn changed manufactures.
Sorry I could have not been more help. Been a long time ago and we just looked at the other end of the pedal (for the "R" and "L") as a kid when working on them
Post the answer if you find out!!! Good luck!!!
