If the guides are worn (which they probably are on a 3.2) you will need to remove the engine and dismantle the top end as already stated. DO NOT just send the heads anywhere, be sure to send them to a machinist who is familiar with the Porsche air cooled engine. You may also discover other problems as well. This is a very complicated and time consuming job and there are many areas where you can go sideways if your not familiar with these motors. I just did this very job on mine along with new cams (20/21
) and discovered many other problems such as several bad valves, stretched timing chains, worn ramps, ect... you get the idea. I was fortunate to have help from Steve @ Dejung Motorsports who put it all back together for me. Nothing like a fresh 3.2! but to answer your question on a scale of 1-10 definitely a 10.