I'm way off the pace. It must be the 86 that has the reservoir cast into the top housing, not the 85.
What i do know is the 83 & 84 use an inverted shock with the reservoir line coming away from the "bottom" of the shock to a canister that is mounted to the frame beside the kickstarter. This is done because there is bugger all room between the exhaust pipe and the aircleaner to mount a fixed type reservoir. Would need to confer with the suspension guru's but i dont think a conventional shock mounted upside down will work as intended, perhaps it does, i dont know. Thanks to a fellow forum member (E74) i have an ex KTM ohlins unit that i am working on from around the same vintage in an atempt at modifying to fit. Looking good so far.