So it has been noticed that for normal street driving, inlet manifold heat, from the exhaust manifold, has a positive effect on driveability & fuel consumption while extractors/headers/flows [pick one] can have a negative effect due to removal of the heat source.

They were clever little buggers those Datsun engineers.

Water heated inlet manifolds are the way to go when extractors are used & I'm trying to remember if the manifolds from the round port 'thrift' versions of the A14 & A15 can be fitted to the earlier A12 type head.

Hopefully someone here will know.

The worst carb icing will occur in temps a little above freezing in high humidity conditions, ... like fog. Particularly in high vacuum cruise mode.

I have had my GX carbs freeze to the point that the throttle shaft stuck & would not close when I lifted the foot from the 'power pedal'.

No dramas though & the throttle closed after about 10 seconds but it was an interesting experience. Covering the lower half of the radiator core with cardboard ensured that a repeat never occured.