I've never worked on one of them if that makes you feel better..... IIRC the 5000 series had planetary drives in them. I know that the bull gear drive set ups in the 1066-3888 (sans the 1566/86 which were also planetary reduction) were good for 175hp. The lighter bull gear set up found in the big frame in the 706-966 weren't as wide a gear, but still seemed to hold 150 pretty decent.
That's a pretty straight looking tractor yet too :Cheer:
Oh yeah, almost forgot there was a serious trans update that was done under warrantee by IH on the 5000 series tractors. Look at your trans dipstick; if there is a new full mark scribed on it then you're fine. Otherwise I've heard that they were troublesome without the update. But, like I said, I've never worked on one either way...