Suzuki GS 750 or 1000. Avoid the shaft drive models.
Bulletproof engines, you will need to refresh suspension and probably the wiring loom and several components like the reg/rec.
If you are going to make a cafe racer you will be changing a lot of the body work but if you intend to use some of them – tank and saddle for example, take a close look at the underside – this is where they rust.
Slightly earlier and closer to the "original" British parallel twin you could try the Yamaha XS650.
I don't know where you get your info but those CB900 engines are about as bulletproof as they come. I used to ride with many people who had them and nobody ever had any trouble.
Told you . Yamaha RD 350 or 400 .
https://search.yahoo.com/search?p=1975+Y...
Any BMW R series.