Asking your questions:
1.- Apart from the serial number and manufacture year, they are the same speakers, sonically, I mean.
2.- If you can find the orange dust caps, the better, because they are more valuable day by day. If you want to buy it just for you, whatever you use will give you the same sound.
3.- I have one of each other, so I tell you it is impossible to find the original orange dust cap. The only thing we could do is buying a black one, put if inside bleach and later finding a spray to paint it and try to match the colour... or buying two black caps. Whatever, if you put some grills on your speakers, no matter what colour is that senseless piece.