You're surely welcome. I'm thinking Case at that time was using up parts that fit both Ag. tractors, while going towards a strictly construction machine. A lot of part changes came at certain serial numbers. Even my newer '79 480C has certain parts that were different at certain serial number breaks.
I've found it's much easier to find difficult parts for them by searching the part number, if you can find one on said part. And, if said part was used on a Ag. tractor also, if it's a dealer item only, prices of those parts are generally 10% cheaper through an Ag. dealer, than through a construction dealer.