just had a thought about this, if you want an original look at the rear, you could use the uk style 500 four indicator brackets that fit on the rear frame and use the bolt that holds the mudguard on. They dont use a grabrail at all, but the usa 500 did, and looks very similar to the later bikes except the indicators mount on the grabrail but importantly are a different size to later f2 etc, and are much more common and cheaper.