Parts for the 750 PD series carbs can be hardder to find than the 550 carbs. Be persistent and you will find them. The Honda part number and Google are your friends.
The only real difference in the PD carbs between the 550 PD46\650 PD50-51\750 PD41-42-44 are the bodies\jet holders\slides\needle, and needle jets
The serviceable parts. Main, and pilot jets\float bowls\mixture, and drain screws\ gaskets, and o-rings\floats\float needles are all interchangeable with the only a couple exceptions.
1. The 550 carbs do not use the accelerator pump. (uses two #1 float bowls)
2. The metal tubes for the accelerator circuit are only used on the 650 carbs. (o-rings not included in 550\750 rebuild kits)
16011-382-004 VALVE SET, FLOAT was used from 76-99. They can be found for much cheaper though.