I focussed on the surfaces on the inside of each rim, where the tyre seals against the rim. I didn't need to touch the bulk of the wheel. I ground away all individual areas of alloy corrosion and blended smooth the profile, using a 12v craft drill with a fine sanding wheel, hand finishing with 120grade. Rubbed down adjoining good paint areas with 400grade. I treated the bare alloy with a chromate passivator (surface conversion), but only because I already had some through my aviation experience. Then 2 coats each of etch primer, wheel silver and solvent-resistant lacquer, all from Halfords. Then leave it somewhere warm and dry for a week to harden before refitting tyre.
Its worth noting that none of the leaks arose where there was the odd visible kerb scratching. ie each corrosion had crept invisibly under the tyre sealing face and penetrated into the pressurised space inside. The same can happen with the rubber ring seal around the valve stem, which can only be replaced from the inside the rim.