In the attached linked picture on my Honda TRX70 near the pull chain, there appears to be the alternator cap that can be unscrewed and on the bottom side of this gear shaft appears to be the drain plug..

Is this where you would drain and refill with a 75w-90 gear oil? or is this "timing and valve inspection hole caps"? It didn't specify in the service manual?

 

The motor oil does not also act as the gear oil like on most 4 stroke ATVs and motorcycles?