That's something worth looking into, since the B20 and the B21 have distributors that rotate in opposite directions. As a matter of fact, the dizzy in the distributor that I have came from a later 240. Goes right in and works well so far for the past 500 miles, so the vacuum advance/retard should be a direct fit.
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...and the bricks keep on rolling

I've got a B20A. Sure could use that extra "boost".
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...and the bricks keep on rolling

Currently I am running it with the retard disconnected, but did set the timing pretty high until it pings a little under load, about 20 degrees. Perhaps, I should also mention that we only get one grade of gas over here - 97 octane, so setting the timing that high without detonation is possible.

I did notice a significant differrence with the old vacuum advance distributor when the hose had a leak. Slightly sluggish accelaration was noticable, but car ran OK. I heard air hissing when I pop the hood and hit the throttle, and discovered that the vacuum hose had a crack on it. The hose probably came from Gothenburg with the car.

As for the 75 distributor, other than a more stable idle, it does not feel any lethargic compared to the old one with the vacuum retard disconnected. I did a complete rebuild on the motor, so its hard to say if the extra power is attributed to the new rings or the electronics. I guess I'll be happy with what I have. Just got to get used to the now redundant vacuum port of the manifold.

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...and the bricks keep on rolling