It depends on just how detailed you want to get in maintaining the original configuration. To get into details, you will need to use the Parts Catalog from close to when your tractor was built. Depending on when in '49 your tractor was built, the 5/49 catalog Rudi pointed you to is right. A later catalog (also available there) will be needed for a late '49. You can check for a part number in that catalog then check a late catalog to see if the part changed.
Part number suffix changes are usually pretty minor and you may not see any difference. These number changes will be something like going from 12345R1 to 12345R2. Major part changes will have a change to the base number and may be more obvious. Larger castings have date codes but most smaller castings will not.
The more significant part changes will have a serial number effectivity listed in the catalog.