Interesting finds Whitedog. Using the part number from your Spicer bulletin I found.
http://www.4wheelparts.com/Drivetrain-Differentials/Dana-44-Power-Loc-Clutches.aspx?t_c=12&t_s=237&t_pt=101189&t_pn=D%2fS22233X
I hadn't thought that the 55p (passengers) would use the same parts but I guess when they finally came out with factory posi for the 55t (chevy truck) in 61/62 time frame it was probably similar.
