While I'm totally in favor of keeping it Bone Stock, I don't.
BUT, this is EXACTLY why I try not to run a bunch of aftermarket crap on my cars. If you're planning on driving them, especially if you're going to go far in them, this is wise. You might not know exactly, but you can usually find something that'll work.
And I also have a notebook that lists all my mods, and has wiring diagrams (including stuff I added or modded), in the car at all times. I even put part numbers in there for wear items. Brake shoes? Oh yeah, that's part number XXXX from a '78 Volare that still had 3 different options.