That boom was originally designed to 'reef' the main by rolling it down onto the boom... Theoretically you could 'furl/store' the main that way too. Turn the worm gear and roll the sail around the boom as it drops. Not great, though esp since battens are generally perpendicular to the leech, not parallel to the boom.
Cumbersome, not good for final reefed shape, complicates the vang in reefed conditions, and generally not done anymore expect for 'in-boom' furling which is much better engineered than these older setups.
Most such booms have long been converted to slab/jiffy reefing and the rotary mechanism not used.
You have a boom that was made for roller reefing. You should have a crank that goes on the end of the shaft coming out of the boom on either side. When you turned the crank the boom rotates like a rotisserie and wraps the sail onto the boom reducing sail area. It was a very popular set up on the 1950's and 1960's but was prety much abandoned by the 1970's. It was a pretty poor system in that it was slow to deploy, and you ended up with really crummy sail shape once it was rolled, which got worse the longer you sailed with the sail roller reefed.
You would be way ahead of the game switching to a two line furling system.