I would add to that by mentioning that from the photo - while it's very hard to tell - but it appears that the rocker is riding on the "top" side of the valve stem... it looks like there is a 'wear pattern' near the top third of the valve stem tip.
You might want to use a push rod length checker - and make sure that the rocker is riding (use a felt tip pen to coat the valve stem - then crank the motor through a full swing up and down on that valve with the rocker in place) in or very near the CENTER of the valve stem. The "witness mark" that the rocker will make against the coated end will tell you where it's at.... if the push rod is too short - it'll ride on on the top end (intake side) -- too long and it will wear on the bottom (exhaust side) of the stem.
You might also want to check for coil bind as long as you're at it. And check the underside of the rockers to make sure there are no witness marks from the bottom of the rocker contacting the spring. As long as you have it open - might as well cover all the important bases!!
