I recently got the factory build card for my 1958 Gas 550. Another forum member advised me that this would tell me what was factory fitted to my tractor. However, no-one told me how to read them! And no-one as Floyd County knows either, although they did send me spec sheets for the 550 and all of variants, attachments, options etc.

The build card features rows of 1s, 2s, 3s etc. up to 9s, and columns of letters A-Z, with some of the intersections punched out. For example, A gas 550 with 10-28 rears is given the factory code 45-001 or another code (there are separate columns for Factory Code and Code) for same is A2008 P00 but how does it indicate this in the punch marks?? Similarly, if it was ordered with a swinging drawbar, there should be an indication of that, I am told. The factory code for that is P-66 and other code is C20 C50.
There is also another spec. grid on the punch-card labelled simply in each box A to Z. Mine has one punch mark in box A, one in R, two in X etc. etc. but those punch marks are positioned differently within each box.
Any ideas? Thanks.