The ship has incandescent bulbs so there is no need to worry about polarity, just connect it to one of the GI strings (6.3VAC) and it will work fine.
I disassembled one of these ships in order to evaluate the circuitry inside, I was not happy with the way it was looking as you have to break it apart, this caused paint to chip off and light to shine through where it shouldn't, rather than fix it I tossed it and went with the other option which I recommend.
Just cutting the hole rather than disassembling the whole ship as it will save you time, and come out better in the end. The ship has a small circuit board in it, this board contains a small regulator circuit to dissipate excess voltage as heat.
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you wont need this circuit as the GI circuit is the right voltage to drive the lamps; just be careful to stop drilling as soon as you drill through the first half, this will minimize damage to the wires.
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I believe I reattached the wires so that the pair of lamps on each side of the ship in series with each other, and the two pairs in parallel; this is the same way the circuit card operated the two sides of the ship.
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It really sounds more complicated than it is, good luck and please let us know how it turns out.