Unusual things on my 1966 barracuda

Sorry I don't have pics ready. While in the process of restoring a 66 cuda Formula S I came across some things that seemed unusual.

First of all it is a late production of July 1966. It seems to have every factory option available.

It has a white vinyl top which means a lot of extra trim and the windshield rubber is different as it has an extra lip on top. How rare is a vinyl top on this car ?

The fender tag shows disc front brakes and 10 inch rear brakes. The car doesn't seem like it ever had discs or 10 inch rear. Does have disc brake master cylinder with extra reservoir on top.
I think it also has a ( anti-residual ? ) valve in the brake line before the proportioning valve. I'm not sure of the idler arm but believe it is different than on drum brakes but will work on either. How rare it is it for a disc brake car to come with 9 inch brakes all around ?

When removing the exhaust I noticed that the heat riser in the exhaust manifold was stuck almost closed. This seems like it was that way for a long time and had to been a lot of trouble for the owner. I doubt they knew it but intake was extremely gunked up.
This riser seems to be a dumb idea as I think a lot of people will not know when it malfunctions. Is this a common problem ?

When removing the valve springs I noticed that one was about 1/4 inch shorter. It was not broken off as the machining looked correct on both ends. I don't believe these spring were previously removed. It did not seem to effect anything. Has anyone ever come across a short spring that wasn't broken ?

The air cleaner on this car was correct for a CA car in every way except it was black and didn't seem to ever have been chrome. It was never re-painted and I don't know of any application that a black one would be used on. Has anyone else come across this ?

When removing the seats I was under the car and noticed that all 4 studs on both seats had a rubber tube over them. These had some red paint on them,same color as car. I've never seen anything like this buy figured out what they were when dis-assembling another car.
These were the bullet shaped plugs that were put in the threaded holes for the seat belts before painting.
I removed the carpet on a white color car and found a couple laying under the carpet. They had some white paint on them.
These are shaped like a bullet with a rounded end and a flat end. They have a hollow center and that is why they were able to be put on the seat studs in my red car. I'm thinking someone on the assembly line would have had to of done this. Maybe to make it safer to work under car ? Has anyone else ever seen this and are you familiar with these plugs ?

That's some of the stuff I can think of right now and sorry for the long post.