Sorry Bob , hadn't been here for a week and answered on the other site... for any others , it should be a 74 , were resold possibly in 1975 as well
but the same 74 decals.. the chassis seems to be the same as the 73 EW643 with the wide track and rear fuel tank..
I have 1 good one , scrapped one , aware of a couple more on the internet , No one at Yamaha has offered to find out any build numbers for
the fluid drives as the info is on microfiche in Japan , maybe. Since they were not racers, no one has kept track of them over the years.
I only have ever found one drive that leaked a bit. lots of broken shifter supports on 15" models from people trying to force them into gear.
I finally stripped one apart just to see what is inside, as people kept asking me about them.
Ron