Welcome on OSS.
Looks like a Slingshot (cable clutch) 750 engine, 749cc and nipple on clutch cover says '90 or '91.
Valve adjusting with screws = '90
valve adjusting with shims = '91
But of course looks can be deceptive and it could be a Slabby engine with cable clutch conversion. Remove the camshaft cover and look at the valve adjusters and you'll know more.