The Chelsea 410 PTO series has been superceded by the 442 series, which is why there are no service manuals available for the 410. The 442 manual works well enough for the 410, although there are minor differences.
1982 International S1754
Make witness marks on both bearing caps and shift cover showing their orientation relative to the housing before disassembling a PTO. They can often be reassembled in multiple different configurations.
Some air brake chambers have permanently installed cage bolts that have to be backed out until they stop in order to cage the brakes, rather than inserting a cage bolt and tightening it down. If there's already a nut + bolt sticking out the back of the chamber, it's probably this style of cage bolt.