How much you're going to have to change depends on just how much the previous owner changed. Most aftermarket pedals are just bolt on plates which fasten on top of the stock pedal... the most you have to do with these is remove them (sometimes they're epoxied too) and replace the OEM rubber pads on the bare metal pedals.
Worst case you'll need to replace the full arms (the pedals are welded to their respective arms).
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