YOu should be okay, I think. I did mine at about 75hrs, as I recall. I pulled the valve train off and re-torqued each head bolt to the specs that Ronald at RanchHand Supply provided, then re-assembled the valve train and set the valve lash properly. Been fine since, too.
This is a good time to check every other nut and bolt on the tractor – I found loose wheel bolts, and other places that needed tightening or adjusting after everything had “shaken in” for the first 75 hours.