Saw Mill, I don't have access to a 1951 GMC Shop Manual covering your 451, but there is a 1955-59 GMC Truck Shop Manual free to go through HERE.

Diving into that book, there is a cut-away diagram of the 1955-59 450 Series rear axle hub and bearings on Page 661 which I snagged and included below in case the hub and bearing design is the same/similar and could help you picture what you can't see through the hub and brake drum. Looking at that pic, I don't see anything other than the inner bearing and seal riding on the axle load tube, so maybe all it will take is more persuasion as Jerry mentioned above. Let us know how it works out. smile

Perhaps there is one of our GMC Gurus that has the correct resource book with more details about the 1951 450 Series rear hub and bearing??? headscratch
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~ Dan
1951 Chevy 3 window 3100
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"My Grandpa Carl's Truck and How it Became Mine"
1966 Chevelle (Wife's Hot Rod) | 2013 Chevy Silverado (Current daily driver)
US Army MSG Retired (1977-1998) | Com Fac Maint Lead Tech Retired (1998-2021)