I've posted many pics of low-mile original paint/original interior 65-67 Chevelles on other threads here before. The gloss varies from plant to plant, time to time, and car to car, based on the guy wielding the paint gun. With that said, the top of the dash is always flat (and on 65's is a sort of hammered finish, and on 67's is an almost textured finish). But the rest of the painted interior parts are (at least in my experience with numerous original paint 65-67 cars from various different plants) a whole lot glossier than the 60% figure that people often state is the correct gloss level.
It is my personal belief from looking at these original cars (but without any way to prove it) that in 65-67 they shot the interior parts (other than the dash tops) with the same paint as the outer bodies were painted (meaning full gloss paint), but simply laid the interior paint down faster and dryer to achieve less gloss. It is amazing how many different finishes you can get with one paint gun with one batch of lacquer paint in it, just by adjusting the distance between the gun and the part, the fan of the spray, and the speed with which you move the gun. We duplicated the original 67 dash top paint on the first car we restored in 1986 with regular gloss black lacquer paint with a little extra thinner, a very wide fan, a little extra distance and a very fast spray. And it was dead on (and is still on that car today).
The fact that the aftermarket re-paint mix formulas call for lower gloss levels does not neccesarily mean that is precisely what was used on the assembly line. Perhaps GM gave the paint co's lower gloss specs for "replacement" paint in order to insure a better duplication of what their painters were doing in the plant via a faster dryer spray? Or maybe those mix formulae are being pulled from later editions of the paint books printed some time after 1967, after it had become general automotive industry practice to really dull out everything inside the car to reduce glare for the driver??
Another possibility is that, even if it was 60% gloss paint in the vat when it was sprayed on the interior components by Fisher Body, once the body went through the oven baking process (where they cooked the body to flow out and smooth the paint surfaces so as to avoid having to sand and buff every car), it was going to have the same effect on the interior paint as on the exterior paint -- to smooth the surface and increase the gloss level versus how it looked right after it was sprayed on the car. A 60% gloss lacquer paint is not going to be 60% gloss after it is baked in an oven! So unless you have an oven to bake your car in after you paint it, then you would have to use a glossier paint to get the same end result that the factory got.
I'll see later if I can find the prior posts with all the pics and link them here.
