The hushers do not actually change the "valve adjustment" as that procedure is done without the hushers in place. If fresh hushers are in place before checking clearance you will not get any sort of accurate measurement. Being that yours are 22 years old you can be sure they are flattened so before removing the cam check and record the clearance at each lobe. If memory serves you'll want something like .016"-.018" after adjustment. The tolerance is wider if you are just checking for the sake of checking. I don't have a repair book handy but you should have one--it will confirm (or not) what the actual spec is.
Keep in mind when you say--"remove the cam" involves loosening the timing belt so you need to determine if you should renew parts there as well--belt, tensioner, seals, etc.
The shims sit in a shallow tray built into each "cup". There are notches in the cups to gain access to the shims. The "proper" tool for extracting the shims looks like pliers but has a point on each end so you can grab the shim. It takes a bit of wiggling to get the shims loose from the cup as they cling through suction/oil film. A pointy pick tool or two work as well. With the cup in hand off the motor, air pressure will lift the shim out too. Have a micrometer handy for measurement and record the thickness alongside the clearance for each lobe. Add or subtract the amount needed to bring the clearance into spec.
With the cups out of the head I usually use air pressure to blow the little bits of old husher out. The hushers get rock hard and break up into litte bits over time.
Place the new hushes on (the top should look like a funnel)-- reinstall the cups with appropriate shims. Don't be bashful about squirting fresh oil all around. -- Dave