I think it's entirely possible the original post was referring to car rear ends, not trucks. I ran a 3.55 and a 3.70 gear at various times in a 58 Chevy car, and those rear ends interchanged from 55 to 64. They DO NOT fit the truck housing. Dana/Spicer rear axles with the non-removable center housing were used in some GMC applications, Ford, Dodge, and International trucks, as well as several Ford car applications. The one I swapped into my 59 Burb was a mid-1970's GMC axle with a limited-slip Dana type 60 gear.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!