As stated the 103 valve guides tend to wear, so as long as the head is off at your mileage I would recommend a complete refresh which would include all new valve guides. Also, the valve stems should be measured for wear,and if it is more than half a thou, they should be replaced. Chances are the exhaust valves may need to be replaced.
Reseat the valves and assemble the head with new stem seals and you should be good for at least another 100K miles.
To change the guides the head is heated up to about 400F in an over, then the old guides are tapped out and the new ones tapped it - just takes a couple of minutes. It takes a lot longer to actually measure the valve guide IDs using an inside caliper and a micrometer, but most mechanics use a "wiggle test" - with the valve installed and slightly off the seat you wiggle the end of the stem. An experienced guy knows whats good and what's worn.
Last edited by Duke2.6; 05-31-2003 at 11:30 AM.