should be a shallow boss on the sprocket. The boss needs to be inward facing to keep the O-ring chain spaced correctly away from the casing. Can't see any boss on your sprocket so might be a Z1 (non-O-ring chain) sprocket. You've also had the chain too loose which is the cause of the 2 scars on the ...

If you know a turner, you can make one. CMSNL have conveniently provided dimensions

Can't tell you size but is this the part you need? Relatively cheap and available.
https://www.cmsnl.com/products/gasket-f ... _92065081/

I'm no expert on later heads but it looks like your 1974 pic (TK-4) maybe has a Z1000 head fitted? Has a 8mm to 6mm stepped stud been used?

The TK-2 castings were generally used on the earlier Z1 range. I have never seen one on a 1975 Z1B but that's not to say old stock was being used up

There are many slight variations on the Z1 heads. Picture here might help you. You can see it if you look carefully by the exhausts

Beautiful. A credit to you

For the more anally inclined........

Some late Z1 and most Z1A

https://www.ebay.co.uk/itm/134120432710?chn=ps&_ul=GB&norover=1&mkevt=1&mkrid=710-134428-41853-0&mkcid=2&mkscid=101&itemid=134120432710&targetid=2361400006200&device=c&mktype=pla&googleloc=9045783&poi=&campaignid=21697363421&mkgroupid=170400390...

Thanks for your reply, but can anyone please clarify the points with the pictures - The green suppressor in the picture, where does that go and what does it attach to. It is a resistor for the headlight and mounts under the RH coil. Look at the wiring diagram to see connections The long wire coming...

Those are the hazard relay and Hazard regulator

oops.I need new specs. I read that to be 69 instead of 60. Ignore my date comment but could be Jan 1981 (11 mark)

There are date codes on loads of Zed parts.
Mikuni items are shown at bottom of this excerpt.

kev edwards wrote:Gs 750 late 70's.

I would tend to agree. The date code on them is Sept 1976 so would have to be a very early GS model (assuming they are Suzuki)