I grew up on JD balers. Think the first ones I used were 24T, 24W (Twine and Wire), then 224 series, then 336. As I recall, they were basically the same design, just heavier with bigger model numbers.
The farmer I worked for did custom baling and we ran 2-3 balers ALL the time. They were bullet proof if you kept the knotters clean and dry and adjusted. We seldom had to re-adjust the knotters, but that takes some special talent and patience, along with a good instruction manual. The manual on knotters should be available online. They had some wear parts on the plunger, etc, and we ran them enough that we had to replace these occassionally. This would have been late 60s, early 70s.
We pulled them mostly with D17 Allis gas tractors (unsure of the HP), but they pulled them with ease.
I don't recall any issues with any of them dealing with gearboxes or frames, etc. We did have to replace the pickup tines all the time due to wear, but that was a nothing.
I don't have a clue how many bales we did per summer, but it was in the tens of thousands. We ran enough crew that we could pickup 2,000 bales per day and stack.
Ron