I've got a lot of it figured out, but not all. I plan on doing an article for the magazine in future that tells how to read them, but I'd like to have a little more nailed down before I do it.

The punch holes are for the card reader machine, and can largely be ignored, because the corresponding holes are printed at the top of each column. So if you look in the P column, it may have 66, and the two 6 boxes will be punched out below. Since all you get is a copy of the build card, some of this may not copy the best.

If you look on the dealer price sheets that came with your build card you'll see the first column is called factory code. P-66 is for no drawbar, on a tractor without hydraulics and three point, so the dealer would deduct 75 pounds shipping weight and $14.25 from the list price. The last column that is just labeled code is for the dealer. In this case it is C11 P40. Drop the letters and add a dollar sign, and dealer cost is $11.40, so the dealer can figure out his profit margin. P-66 is also for adding the swinging drawbar, so you can see where some of the confusion comes from. Could be that since it was a deduction, the dealer would order it minus code P-66, making the P code 00, or no drawbar or three point hitch equipment. 

Using this, take a code from your build card and look for it on the dealer price sheet. Say your U code is 90. Go through the list and you'll find that is the code for factory installed power steering for a gas tractor.

Not all of the codes show up in the dealer price book, or aren't as easy to figure out. That's the dilemma that I'm trying to figure out now. But this is a start. Post all of your codes, A-Z, and I'll take a crack at deciphering them.