You have had many good responses, but none have commented on the importance of correct valve clearance. (some have even suggested the opposite) You don't seem confident yours are right. Spend a little time there. The proper clearance has an effect on valve TIMING! If the clearance is too much...the valve will start to open later, and will close earlier, therefore it IS important.
I'm unfamiliar with your tractor, but it should use the same procedure as other 4 cylinder tractors (if it is a 4 cyl). With #1 piston on TDC on the compression stroke, adjust valves 123&5. Rotate the engine 180 degrees and adjust valves 467&8...valves numbered from front to rear. By doing it this way, you can be sure the follower is opposite to the lobe on the cam.
Just to eliminate the possibility of sticking valves, lubricate the stems with your favorite magic potion while you are there.