You really wanna get all the guides replaced regardless for oil consumption reasons. The valve stem seals mask the oil consumption due to worn guides. The guides usually last 100k, but don't cause issues other than oil consumption anyway so new stem seals usually holds you over until the heads off.
I recommend you find a good machine shop (emphasis on good with experience /w older MB head's) and have them just do it all for you. Supply them the parts. I had my head skimmed, cleaned, pressure tested, valves lapped and guides + seals replaced for $215 (I supplied parts).
My guy did a great job:
