I am refurbishing the door hinges as part of a total body restoration.
Basically back to bare metal, new pin & bush, then paint.

Do people recommend having them zinc plated to stop rust occurring where the two parts rub together?
Is there any down side to having them zinc plated prior to assembly then painting?
Do you paint the hinge on the car with doors, or as separate items off the car (which is what I have done in the past)?

Is it necessary to use a reamer on the bush, or will the correct size drill do the job?

Any comments, thoughts or procedures on this job appreciated.

having them coated would make them more weather proof but it would also close the tolerances in the hinge pivot but it will wear down eventually and rust will follow still.
i have been looking into alloy hinges from uk.
as for painting on the car it all depends on the paint your using.
because they run a gasket between the car and hinge building after makes 100% sense but if using metalic, pearl ,flake or a very pale color it is higly recommended to have all the car together in its hanging position and paint all in one go as the paint will fall even and hopefully have no variations
but if using a solid color will not effect

No need to ream the bushes, they come pre-sized for the 1/4" pins.
However, they are only 5/16" OD, if the old bush is worn right through by the pin, the hole in the hinge is now oval and a new bush won't fix it.
But it is possible to drill the hinge centre bit out to 9.0mm and machine a new oversize bronze bush to fit.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.