To tell you the truth, its all comes from experience. Lincoln offers no short cut.
The code for your machine :
http://content.lincolnelectric.com//pdfs/products/navigator/im/IM142.pdfThis manual covers codes 3400 and below, but will show you some differences in the armature bolt up, etc. You have to look at the top of the page to see what went with each code number. This is why we ask your code number when you ask about parts, etc.