What rear is currently in the truck?
I don't know about your 55, but the later GMCs had Spicer rears which would not apply to the tech tip referenced, although a ring and pinion swap should be possible.
"Do not walk behind me, for I may not lead. Do not walk ahead of me, for I may not follow. Do not walk beside me either. Just leave me alone, you're starting to freak me out."
1957 GMC 150
| 
