My car isn't a '70, a '72 and it came from the factory with the body side mouldings.
Since the car is mostly original, I'll keep them on. It does make it harder if I want to add stripes as it messes up the '71 style R/T style lines and it's in the way of a '70 stripe unless I take off the top thin stripe.
One thing the body side moulding did is from what I was told, it eliminated the side louvers on my car as my '72 is a Rallye (JS) car and did not come from the factory with the body side louvers as verified by the original owner and the car still has all the original body sheet metal.
The factory body side moulding often can be identified by the squared off ends which you usually don't see reproduced as the aftermarket stuff ususally has tapered ends.
Despite the body side mouldings taking away a bit from the sportier look, I'll probably keep them as they as factory and once I get the car on the road it'll help protect the car from door dings and such in parking lots.