4 or 2 wheel? doing guides means the heads come off, doing a timing chain is worth it at 120k, front of the moter has to come apart, and the tranny needs disconnected to do the rms, i guess its 6 to one half a dozen to another, youve got your work cut out for you weather you do a r&r or a teardown, why would you just replace the valve seals? why wouldnt you check for valve guide wear and possibly send the heads down to the machine shop? and if your goin to do that you might as well send the block to for a clean and check for cracks, hone, and new pistons and rings, your going to have a lot of money into what you want to do, and if your doin it yourselfe why not have a fresh moter instead of just heads and a couple of seals, an engin kit and a machin shop lookover and youll be verry happy when the wallet fills up again