I suggest that if you put a vacuum guage on the manifold of the engine that has two Weber/Solex/DelOrto carbs, & has a cam to justify them, you will find it has no vacuum to speak of anyway, so the disributor should have already been set up for this engine without a vacuum advance canister fitted & the vacuum advance plate locked down.
This is why the triple Weber equiped Bathurst Chargers had no vacuum boosters for the brakes, .... no bleedin' vacuum.

But for basically stock engines that DO develop good vacuum at cruise, the retention of the vacuum advance feature is a bonus.

Generally speaking, the coolant bypass port in a Datsun engine is too small to cause overheating by virtue of it causing the coolant to circulate only within the engine itself.
That business about coolant traveling too quickly through the radiator to shed it's heat is just an urban myth. If it is too quick to shed heat, it's too quick to pick up heat from the engine too.
With the thermostat wide open the radiator does its best work & that's a practically unrestricted flow.

The removal of the thermostat from an otherwise serviceable cooling system will usually result in overcooling. [big time]