I would think that puts you in a more flexible bracket as you have the option of using either IT or YZ 250/465 wheels and if you do go for the 81 onwards you dont have the bearing, axle bushing, and brake plate issues associated with the one off G model set-up.
I think the 250H wheel offered will get you out of the woods at quite a reasonable price.
The quickest way of identifying the G model hub is the axle size (the brake plate to match will also have the smaller bore for tha axle naturally, same for the bearing spacer).
The spacers play havoc with your head too, Yamaha started to make slight adjustments to the length of the casting on the brake backing plate and shortening the steel spacers to suit the new Plate as year models changed. If you get a G,J and K rear hub together you can easily fall into the trap of deciding there is no difference except the part numbers quoted from Yamaha, but when you get down to putting the whole lot together you find the subtle differences will send you straight to the hurt locker - do not pass go, do not collect etc.
The other thing that is chopped and changed is the quantity of bearings fitted to each model, check out any number of parts diagrams available on the net and you will see what I mean. This is really one time that the part numbers actually denote a change that will result in some form of incompatability.
Cheers Jason