Latest update. Finally soughted the brakes and tuned the Fox forks. The handling is fantastic combined with the Ohlins rear. I've had a lot of big bore bikes, most makes, and this motor is the sweetest, easiest to ride of them all. 13/53 gearing, electric smooth with heaps of torque and still too fast for a fat old bald guy like me! I think the engine is even better than the last XC500 I had. It turns a good as anything I've ridden. My only qualm is the weirdo shaped kick start lever, as you only get about half a decent go at it because of the design. It starts easy enough, if you go through the procedure, but a stall in a race and she'd be all over. I can see an '84 kick lever in the future. I'm not that much slower on it than my modern bike (2008 Husaberg FE550) and I'm sure it's only because it doesn't stop as good and you can't be as aggresive into the corners. I have a '76 360 and a '74 400 as well, if the engines are similar to the 390 they will be great bikes too. I also have a '78 roller and have been deciding on which engine to put in. At the moment a 390 engine is on top of the list, maybe with the 420 power up kit.
Cheers,
K