Are number matching or original components a big deal?

- somebody replaces a oil burning 273 with a 6.1 hemi, do you think the car's value went up or down?
- somebody replaces a 7 1/4 with a Dana 60, do you think the car's value went up or down?
- somebody replaces single exhaust with a TTI dual exhaust system, value up or down?
Point is, it depends on the car. I say if you have a numbers matching 340 car, or anything that's a factory "declared muscle car" (Charger R/T, H-code, Road Runner, Super Bee, even a 360 4bbl Duster), better off with at least SAVING the numbers matching/original equipment stuff. Doesn't mean it has to be on the car.
In my opinion, anything that's newer than 1961with a 2bbl V8, or slant six, have at it and in most cases the value goes up.