Tom,
I have an XR style seat from Omar's. It looks great, nice gelcoat finish. However, the seat cushion is very hard and also narrow. I doubt I can do more than an hour on a bike with a seat like that, especially with stock footpeg position, as all the weight will be on your ass. With mild rearsets, somewhere around the footpeg mounting studs, it may become a bit more bearable. If you plan on any long rides, perhaps a "scrambler" kind of look, using a SR500 seat from Motolanna would be a better choice. Their "Classic" seat is wide enough to fit over the frame, and just short enough to let the frame loop show. If you have a "later" model (74 onwards?), you will have to cut off the seat latch/lock housing, and possibly the hinges also. With a short alloy rear fender and smaller taillight and indicator lights, it should look good to, IMHO.