I thought I'd seen this somewhere, and sure enough I found in the '58 supplement (but not in the 1956 manual!) "do not use hypoid lubricant" which I assume means that there is "yellow" metal in the steering box and therefore one should use GL-4 or lower (not GL-5 or GL-6.) correct? I'm talking about a Saginaw integral box, BTW.
nate
(reason I ask is, I've got about a half case of Redline Heavy Shockproof laying around... but I'm fresh out of MT-90.)