The part number for the McD knife head in my earlier post was MC139 NOT MA139 and I see on Balster's website (BTW - I thought they were out of business) that both heads were meant to run on McD mowers
5' MA139 st. McCormick US Mower
7' 462378R11 (458-969 Reg. Sec. Sickle) McCormick US Mower
6' MC139 McCormick US Mower
7' MA999 McCormick US Mower
7' MC139 McCormick US Mower
All the Amish repair fellows tell me the 139 is the light duty one, the 999 is the heavy duty one. They both work on the #9 mowers that I have.
McCormick is part of International Harvester. International Harvester was purchased by J. I. Case. Case is now owned by New Holland, and is called CaseIH. New Holland is owned by Fiat, an Italian company.
You can still look up parts for your McCormick equipment, on line, by going to:
Part Store CaseIHHope this helps.