Just as an aside to all this, the 85 Cab has a crude mechanical/vacuum system. I scrapped mine long ago, its ok when new, but not good as it ages.
The tiny brass strip flap valves don’t seal any more and speed can’t be held.
Of course these tiny bits can’t be bought so you’re faced with buying the complete unit – if you can find one.
Anyway, taking the big vacuum cylinder out means more airflow across the engine which is good.