'57 Napco 4x4
 

Where these made in the factory or where they shipped out and converted?

shipped out converted and shipped back to the gm dealers

napco=North Western Auto Parts Company

heres a place with all kinds of info on them
http://www.napco4x4.org/

Thought so. Guy over at CTS said they were made in the factory. I don't think they did that until the mid 60's.

They were made at the factory in 56 for GMC and 57 for chevy.

lol@me i was wrong :lol: and i just got done reading all three pages on the napco history and that was quite interesting :metal:

..

Look At Door Jam Plate!!!!!!!!!!!!!!!!
 

There Are Both Line Built And "after Market" In Those Years. You Could Add A Unit On Later. I Think They Bragged About Only Four Bolt Holes To Drill. The Rivet Deal Is A Good Indicator, As Already Said. Another Good Way Is That The Gvw Is About 600lbs More On Line Built. I.e. If You Have One And It Says 5000 Lbs On The Door Plate It's Not Line Built. If It Says 5600 Lbs It's Line Built (basic Number Will Vary Depending On Chassis Type)