Update: My stock IH (whatever part number?) belt proved to be too long after a couple of mowings... I replaced it with a Oregon 1/2 x 76" Kevlar belt (
http://www.amazon.com/gp/product/B00...?ie=UTF8&psc=1) that just barely... and I mean barely... fits...
I'm thinking the right way to go is the same kevlar belt, but in 78"
http://www.amazon.com/Oregon-75-478-...+1%2F2+78+belt
The 76" belt allows NO spring tensioner travel at the mule drive and requires the idler adjustment to be backed off 100%... Even at that, it's a challenge to get it on the deck pulley...
That said, she doesn't slip... I have literally mowed down thick weeds taller than the hood, at typical mowing height, at about 2-3mph without stalling the tractor.. The cut quality was poor (left most of it about 6" tall), but a second pass cleaned it right up.
Mowing "normal", but lazy man height grass, she just eats.... The pulley is well worth it. Now I have one of my 50As on site (already has the smaller pulley!!!) and am just saving my pennies for the meg mow blades. It should be a nasty animal with that setup.