I'm guessing you mean the 87-90 year version? Does it have the paralever?
From Micapeak page:
During the period 87-90(life time of the first version of the paralever GS), the first G/S version continues with a smaller engine (650 cm³, 82mm x 61,5mm, 27 hp (20 kW DIN) at 5500 rpm, 43 Nm at 3500 rpm, Compression: 8,4:1, 2 Bing carburators 26mm, 5 speeds), it's the R65GS. It is exactly like the R80G/S except for the chrome exhaust, the GS mirror, the battery (12v/20Ah vs: 12v/16Ah) and the weight : 198 kg.
You may ask from HPN or elswhere airhead aknowledge people if the 1000cc big bore kit is fittable to it. If yes it could make a good machine i guess(?)