I am looking into purchasing a used exedy twin disc and getting replacement discs?
Would I need to do anything else other than getting replacement discs such as resurfacing the fly etc.?
Any reason why running a used clutch would be bad for the car?

 

you may want to resurface the fly wheel

 

Id let a shop take a look first and tell you what needs to be done. Id hate to pay for install twice on that. Id agree about the fly though, its probably time since the discs are done.

 

As long as all the consumables are new, then you should be good to go. Like the others said, you don't want to pay for opening things up more than once.