Hrm... Five lugs... Sounds as if she's been modified.
The VIN/Serial should be longer than JP2013. The VIN on my '46 is longer than that, and the ones on the Advance Design trucks are longer yet.
It should look something like this: 3JPL35574
3 = Detroit Assembly Plant
J = 1951 Model Year
P = 3100 Series (1/2 Ton)
L = Month of Manufacture (December)
35574 = Serial Number
For a 3/4 ton, the P should read R.
It might be on the title, but back in the day it wasn't uncommon for the truck to be titled on the Engine number, instead of the Serial number. Definitely check the VIN tag. It should be in the driver's side door riveted to the frame.
A GM Shop Manual will be indespensible for most things, (at least, if they're stock) and Tom Brownell's book is cool, too.
If it's got a non-standard Engine and/or Tranny (235 I6, V8 of any displacement/make, SM420, T5, et cetera), find out what it's got and get a shop manual covering those components. Sooner or later, he'll need to know how things are put together.
