Matt Gonitzke: Thank you for posting the service bulletin, I think have the same bulletin; it came in the box with a new spindle I bought from the dealer.
If I'm interpreting it correctly, it appears that IH made decks with the water-pump style bearing, and that the aluminum-bodied re-buildable spindles were an MTD/CCC innovation. Further, the water-pump style spindles (IH P/N ST-745) were no longer supported, but replaced with the new assemblies which included the pulley.
I also note that the production of the xxA decks overlapped the production of the xxC decks for three years, 1979, 1980, and 1981.
From your text I draw the conclusion that the only difference between the "A" and "C" decks is the thickness of the drive belt and hence, the width of the pulley.
Do you think, or does anyone recall, if the introduction of the front "patio" wheels coincided with the abrupt change to the "service kit" re-buildable spindles, i.e., about 1987?
By the way, I didn't mean to communicate that I didn't believe either you or Dennis, I was merely trying to spur you to "present evidence" to support your claims. You'll have to excuse me, I've been serving in a jury pool all week and I have been subjected to several lectures about the rules of evidence, reasonable doubt, etc.
Finally, for Keith Ostendorf's benefit, if he or someone else installed a 3/8" pulley on the 44C deck, it could be P/N IH-126393-C1 at 4-1/2" diameter, but he could have the belt designed for P/N IH-59703-C2 5" diameter. Parts Lookup only calls out one P/N for the belt, 954-3004, but Charlie's FAQ lists two, one 78" long for the 4-1/2" pulley, and one 79" long for the 5" pulley; the length for P/N 954-3004 is not given.
I also note that the "speed-up" pulley is not called out for the 50" deck; I guess the IH engineers figured the 44" deck could take the "speeding up," but the 50" decks could not.
Thanks for responding, we now have supplementary manufacturer data that helps explain why owners like Keith keep asking questions and why the answers from people like me must seem so confusing.