I am all ready to install the new valve guide that was supposed to arrive yesterday. My exhaust guide failed on a cylinder that fouled plugs. When I was replacing the seal the guide lifted right out. My repair guide says to heat the head up to 174-194 degrees and cool the new slightly oversize guide with liquid air or dry ice. I'll be heating mine in a little makeshift hot air oven and cooling it in a bag surrounded by salted ice. If I didn't already have the head off for another problem, I would be tempted to run the engine and have a cold oversize valve guide ready to put in. It's more time consuming than I expected removing the head, because you have so much stuff to clean and keep clean. That's assuming your valve is too loose like mine. If not, I know that some shops don't bother with heating and cooling but use a little air powered "rattling" device. It seems like in the long run that could do more harm than good, but you can think about it if you're doing a bunch of cleaning...
I have read some people think there should be no loosness between the guide and the valve stem but it would seize if there wasn't a tiny bit of room around those fat stems.

Hope you have an easy time of it and don't have to remove the head -it can become a can of worms!

Basil