If you own a TC with the ultra rare 16v Maserati engine (head made by Cosworth), and your valve guides are original, there is about a 90% chance they are shot.  Especially if your TC has more than 10k miles on it.  The Maserati/Cosworth head is an *amazing* piece of Engineering prowess, however, this head has ONE single fault....the exhaust guides.   The factory used a poor quality phosphorous bronze material which (over the years) degrades and the result is a loose valve.  Loose valves can cause all sorts of problems if not rectified.  
RDI Performance's team came up with a solution to this issue about 25yrs ago.  Our new manganese bronze guides are an exact copy of the factory guide, just in a far superior material. 
 
We have been rebuilding 16v Maserati heads since our first build in 1994.  Over the years we have noticed that 80% of the time (depending on the mileage and oil change frequency the customer did on that engine) the intake guides are fine, but the exhaust guides are shot.  So, if you are planning to rebuild your 16v cylinder head, you will want to pick up quantity 8 of these.  However, if you want to be safe, and order 16 of them (so you can replace your intake guides too) that is your call.   Price is per one guide.