Hard one Muskrat, the usual stuff applies in that you dont know the internal condition etc etc. The fact it has a carby and maggy on it adds to the potential value.
You would have to sound him out a bit and see if you can get some idea of what he thinks its worth, maybe start at somewhere around the $200 and see how he reacts. If it was put on evil bay it would probably go for many times that amount.
Good luck, just hope it not one of those "nah mate, I'm going to do it up oneday". That really pisses me off, I know of quite a few good bikes that are going to be done up oneday and never will.