My buddy Ken H. is a local legend who bought his Metallic Green '69 Charger new, ordered will all the goodies sight unseen from Vietnam in '69.
He's not totally right but the car helped him through it, both dreaming about it while in the sh*t, and later as he's been single his whole life, the car is his first and only love, his whole house and garage devoted to the car, wild racing parts all over the house, living room, bedrooms, closets ;]
He'd never street driven it much, just mostly drag racing with some insanely impressive slip times, and a garage queen it's whole life, never driven to commute.
By the time I met him, the interior was out, it had a fuel cell, Holley 120 GPM pump, some monster carburetion and headers, Centerlines, a spool, fiberglass front end.
We were virtually neighbors and he helped me with my Roadrunner project with his knowledge and garage space, then we became friends and we started doing movie nights, a bromance.
We had a Mopar club here he was a highly respected member of, and for someone to have told him his car wasn't numbers matching because it was modified would have been a joke, because even highly modified it was still a numbers matching car with the original block and trans.
Most of the cars in the club had performance modifications, just about anything you can imagine, and I showed my car in the B body Modified class, 3 show trophies, last one in 1991, 1st place in it's class. *
The modified class doesn't give a crap whether your engine is original or not, and plenty of cars in those classes are numbers matching, it's just that the owner prefers his performance and more importantly cosmetic mods.
All those other parts can be replaced back to original again, should you care to, but numbers matching means something
matching a VIN, when applicable, so we're talking block and trans casting here, nothing else.
Any axle housing, manifold, carburetor from a swap meet can be swapped back in to a car to make more "original", but the block and trans are the only two pieces that really matter.
Obviously with anything expensive - Rolex Subs, '59 Les Paul Flametops, 4sp Hemi Cuda Convertibles, you have to watch out for fraud, as there are ways to fraudulate such numbers. Fakes abound. There's more '59 flametops Les Paul floating around now than Gibson shipped, and if you can find their missing shipping ledger, they will pay $59,000 for it because of the dang counterfeiters still busy making more.
An X Ray would reveal if the area has been ground, welded, machined, and restamped like people did with the rare Singer Sewing Machine made WWII Colt 1911 sidearms, only 500 made. X Ray inspection to determine authenticity if provenance is unknown. At a certain price point it just becomes mandatory.
For the record, I'm not disagreeing with anyone here. This is been an open/closed subject for decades.
* The engine compartment got me the trophy, people barely looked at the body or interior, which was a little sad but probably good because I did the work myself with a backyard painter. ;]
Sent a bunch of stuff to the platers including fender bolts, pulleys, polished the radiator, it was stunning as well as balanced and blueprinted. Electric fans. Transgo Stage 3 on the street. Giant cam, Jan's 11.25:1 pistons, all used parts from local drag racers.
The .525/304 Isky bumpstick came out of local legend "Sugarbear" '69 Roadrunner race car turning impressive times with 300lb guy on board.
People were begging me to take it to the strip, telling me "I needed to take it to the strip" and I refused, too pretty, a 383HP I spent two years building, no thanks.