Yes, an engine can lean out enough to overheat, but only under full-throttle, max load conditions, like pulling a heavy load uphill, with a vacuum leak, a partially restricted fuel passage, etc. It won't happen at idle, even with late ignition timing.
I'd suggest getting a can of Kroil from Kano Laboratories in Nashville, Tennessee, and give all the valve guides a good squirt from the top side, through the valve springs. If there's any varnish buildup, the Kroil will loosen it in a matter of a couple of hours. Adding a little to the crankcase oil won't hurt, especially if you run a few miles, then change the oil and filter.
www.kanolabs.com Jerry
