I would just replace the hydraulic tappets if going that for, If you are stripping the head down to a bare casting and having the guides replaced just get the machine shop to chemically clean it afterwards, main thing i would add is that cleanliness is very important and after any machining has been done clean out every nook and cranny to make sure no swarf or dirt is there to ruin all your hard work, I put my own engine together but had the block and head cleaned by the place doing the machining, also be carefull of the studs in the cylinder head the aluminium is a lot weaker than the stud and to much force will break the casting, I had one exhaust stud that caused grief and had to pay extra to have it removed also had to have a little welding done on the head because of it.