If you were to want to do it yourself, follow the following steps.
1)Disassemble keeping all valves, springs, shims etc indexed. If you mix them up you need a valve job.
2)Clean the head thoroughly, then check for flatness. Every service manual for every car tells you how to do this. The problem will be finding a straightedge flat enough. Machinists straight edges are about $100.
Spec: .0015 max warp.
If the head is far out from this, it will need substantial work. The spec for head grinding does not allow much material to be removed, so you will need to have the head baked in an oven under tension and brought flat. Most likely not worth it.
2)Check for valve guide wear by placing a bit of hose on the valve stem and inserting it into the guide. The valve should rest on the hose and be above the seat between 1/4-1/2 inch. Place a dial indicator with a magnetic base on the flat steel bench you are doing all your work on (right?!?!?!) with the indicator tip pressing against the side of the valve at right angles to the head. Preload it a bit and zero. Wiggle the valve gently back and forth, recording the total movement of the valve on either side of the zero, then add them together and divide by two. Spec:
Intake: .02-.05mm Exhaust:.05-.09mm
Limit Intake:.1mm Exhaust:.15mm
If the guides are out of spec, you are done. When the new guides are installed (by you or a machine shop) the seats will all need to be reground/replaced to make them square. If you do not replace the guides but merely install new seals, the seals will hog out due to valve stem movement, and your head will leak oil.
2)Check the margins on the valve with a dial caliper. When you grind the valves, this margin will shrink so if you are right at the limit already, buy new valves. The exhaust valve margin is especially important on our turbo charged cars. Do not skip this step! If your exhaust margin is the thin, the extreme temp/pressure in the cylinder will cause it to literally disintegrate, and then little bits of it will shred your turbo/pistons/cylinder walls.
Intake: 1mm Exhaust:1.5mm
Limit Intake:.5mm Exhaust:1mm
3)Clean the valves with the wire wheel on a bench grinder and inspect the valve face (where it contacts the seat)This area should be flat. If you have access to a grinding machine, follow the procedure for the machine to grind the faces flat, then remeasure the margin. Replace any valves with insufficient margin. If the faces are flat, skip to step 4.
4)Get out your tub of lapping compound and suction cup on a stick. Put the lapping compound on the face of the valve and insert the valve into the head (remember to take the hose off from the guide check) Put the suction cup on the head of the valve and spin it back and forth. The noise it makes should change after a few seconds. Pop the valve back out and clean up the face of the valve and the seat. Get out your dial caliper and measure the band the has appeared on the seat.
Spec: .9-1.3mm (.0354in - .0511)
After you have measured the mark on the seat, look at the face of the valve. The band on it should be right in the middle of the face. If you ground the valve, it won't be. Get out your angle cutters from Goodson
($800) and follow the instructions for seat grinding (too complicated to go over here) or send your head in to have the seat ground.
If people want I will go over valve stem installed height, spring installed height, spring squareness etc, but not right now. My opinion is that the best you can do at home is determine if a head needs work, not do the work yourself, unless you want to invest some serious bucks on equipment and do head work on the side. Basically, if your valve faces are flat and not hammered into an angle like \_ (should be like this \), your margins are good and your valve guides are within spec, double check your installed heights, spring strength and squareness, throw some seals on it and go.