I have a manual around somewhere that describes the codes and how to cut the key for each tumbler pattern. I think the original keys had a knockout that had a number stamped on them. I think the number was on file somewhere along with the code.

1951 GMC 1 Ton Flatbed -- It is finally on the road and what a great time I have driving it!
1951 1 Ton Completed

My Chevy Master 4 Door is on the Road!