The carburetors arrived today! I got extremely lucky with this set. nismospek is correct in that the set (carbs, isolators, manifold, stacks) was sold by Datsun Competition. Everything mentioned by the seller, including that they were only driven for <100 miles, seems true. Only missing a few easily sourced pieces. The throttle shafts have zero play and the carbs look as though they sat for only a few years. They need some cleaning, some of the plating is faded, but all in all they are seemingly an extremely mint and unmolested set!
While craigslist can commonly be extremely risky, sometimes you just got to take a leap of faith! In this case, I lucked out.