Two things, generally when it comes to brakes and tires there two things will not harm a car's value at all. In fact, disc brake conv. are one of the very few mods that one can make that most often increases a car's value. Along with steel belted radials.

Second, as Bob S. suggest above, keep the old parts. This way you are offering a new owner the best of both worlds and how could that possibly hurt?

Generally speaking if an upgrade is done to a car and it is truly a bolt on item, it will not harm it's value. In saying this, if the correct/original part is a numbered part, hard to find or very rare, then this could be a factor as it could be impossible or seriously expensive to find/replace.

A good example of this would be an original intake that has been replaced with an aftermarket. Yes, this is bolt on, however, if the person did not keep the original intake the new owner would then have to find one etc. to make the car correct and yes a serious buyer would take this into consideration when looking at the car and making an offer.

Spending my days at my friend's house who does appraisals for a living and has been doing them for moer than 35 years I tend to pick up on stuff like this. Just thought I'd pass along his advise that he always offer people in this situation etc.