What is the reason for changing guides?
If they are worn you have a few options but would need to measure the guides to be sure they are actually bad. Usally its just worn seals blowing oil.
If your changing to smaller stem valves the guides may be bigger od than the new small id guides. If that makes since.
You can see if they have bronze guides witht he valve cover off and a strong flash light. If its bronze its replacable. Only real way to be sure since many engine builders will drill out the stock guide bosses with porting or valve/seat replacement.