This is a really good spoke calculator and helps to visualize everything: Freespoke
For a Marge Lite rim and Surly New Rear Disc hub, 17.5 mm offset and 3X you would use 262 mm on the left and 264 mm on the right side.
For a Marge Lite rim and Surly New Rear Disc hub, no offset and 3X you would use 262 mm on both sides.
So left side spokes can be reused.
262.4 mm is the optimum length for right side on the non-offset build, so 264 mm would be only 1.6 mm too long. I would give it a shot, perhaps with nipple washers added to right side spokes to prevent them from poking through.
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