Success! (After a fashion). I fed the main feed wires up a groove milled in the mast, these were soldered to two strips of self adnesive copper foil, one either side to act as 'bus bars'. The tails from the grain of wheat bulbs were then soldered to the copper foil. Insulstion was achieved by painting the mast. Not the neatest of work but the best I can do with banana fingers....

In the past I have used a slitting saw in the milling machine and then run 2 enamel copper wires to the light, the reason I used enamel copper wire is that it is much thinner than plastic insulated wire of the same size.

My first attempt tapering and grooving the mast failed miserably. I made the groove on the mill with a 1/16 round nosed endmill, but pushed my luck an went too deep. When transferred to the lathe for tapering it shattered, and I only had 2 inches projecting from the collet.
Plan B. 6mm dowel is to thin to groove, even to just half it's diameter. Hunting round I found a piece of 8mm dowel just long enough for the job. This time grooving and tapering was much easier, and at the end of the day, only I (and you guys) will know I cheated a little and made a slightly fatter mast. I have set two feed wires into the groove and will now bury them in filler. I will 3d print a mast foot to ease fixing the mast in place and possibly a tiny junction box for wiring the actual lights to.

Hi Nick, As the original had wooden masts I suspect any electric lights fitted would have had insulated cables running up the mast supported by some form of pin attached to the mast. I have used insulated copper wire used in transformers etc as this can be obtained in thin grades. As it's insulated you can run the wires together and just scape off the coating when soldering to the Led. If you use a bit of heatsink over the joint this will simulate the waterproof seals used. I did buy (from Component Shop) at one of the shows some very fine insulated wire. When I say fine I mean its not much thicker than a human hair. Worked fine for Leds but not sure it would be OK with grain of wheat bulbs due to the current drawn. I usually paint my wires white to simulate the fire retardant wiring used on naval ships. You can get 2mm Leds as well as surface mount types which work well in restricted spaces. You can solder your feed wire to the small tab at each side but test that you get the polarity correct.
hope tis helps but please let us know how you manage to proceed
dave976