I don't know anything specific about the socket # you reference above, but most of the repro houses for these cars indeed sell a 2 wire replacement socket, which is incorrect for the car if you're a purist, but is guaranteed to have a more consistent ground than the original if properly installed. In fact some of us who value performance over originality have put effort into running a dedicated ground wire to all of our lights to permanantly eliminate all grounding problems back there...and the new 2 wire units like these will take much of the hassle out of such a mod: http://www.classicindustries.com/firebird/parts/a13558.html
Rock Auto sells the same replacement for $2 if you want to save a few pennies, they charge less for shipping too on small orders.
