In the shops where I worked on all make of engines we checked or set the valve clearance using this method:
When the exhaust valve is fully open you check or set the intake valve clearance.
When the intake valve is fully open you check or set the exhaust valve clearance.
Trouble with Gravely and other engines is the pounding action of the valve stems into the lifters causes wear on both parts. This wear can cause an error when you check or set your actual gap.
Thanks, I'll try both methods and see wich one works best on this beast.
Sounds like these were made for leaded gas.