There must be a glitch in a database somewhere as lots of different firms advertise rear brake pads for this drum braked model and say that I am wrong if I ever point it out. I have given up caring. This one caught my eye though, not only do they think that a 1974 750S has a rear disc brake but they also think it is on the right hand side!
https://www.ebay.co.uk/itm/Moto-Guzzi-750-S-1974-Brake-Disc-Pads-Kyoto-Rear-Right-Pair/112847675065?epid=754583636&hash=item1a463edeb9:g:kwAAAOSwy6hamqzR
These ads really annoy me. They list brake pads for every model for every year produced, when they could do the same with one ad and a drop down menu to pick the model. There are currently 26,858 ads for Guzzi brake pads listed on eBay!
Maybe they think we’re not buying enough of them! 
Probably the same people who sell sprockets & chains for shaft drive bikes. And they’ll list 'em for not just every model & year but colour too!