I know they came with 79 DOHC and on some 78SOHC bikes.
Than there were people who use tubed Comstars to run tubeless, general opinion is that being risky to some extent, the tire rim is different.
Maybe the PO was one of those people?
Tires are for a long discussion, I used a set of BT45s and was very happy with them (one front and two rear tires, total 12 000 or so miles)
But when I needed new set for long trip, I bought a set of Shinko 712s and they served me well through Tail of Dragon and ever since.
Than there are people who run or did run Kenda dual sport tires on CB750 - Andy750 is one of them I believe