I have a 75F which is the forerunner to the 76F. They are virtually the same. Some could say the 75/76 were first or at least early production "cafe style" bikes. A cowl rear seat, 4-1 pipes, relatively lower bars. But the 75 400F may have been the first, or at least tied. And of course you run afoul of the purists who might say what's a production "Cafe style" bike anyway. Cafe styles come from the owners, not the factories, etc.
Highly unlikely it skipped a cog on the cam chain. That's just not something that happens. Cam chains break altogether, and sometimes a cam will twist in half from poor oiling, but that's 99% of the time after an overhaul where the builder used silicone sealing product.
I'd want to know whats really wrong with the engine. Get it out in the light, pull all the tappet covers and the ignition cover and turn it thru some revolutions.
Oh yeah, not particularly rare either, IMO. Quite a distance from sandcast which were primarily 69 and possibly a 70.
Unless the chassis is in great shape, and its not, with a bum engine I'd say $300 to $500 tops. I'd prefer to get it for less even. Even if it looked great and was low mileage, age takes its toll on the rubber parts, fork oil, shock oil, swingarm bushings rust up, cables corrode internally, instruments get moisture inside, carbs are a wreck, gas tanks are rusted, etc.
