I am also planning on dyeing the black carpet in my 83'. I found some dye on the web that is supposed to be really nice, but it was $120/liter (yes liter, not gallon), so I am going to try some spray dye that I got from Pep Boys. I will take some before and after pictures and report back.
i used to detail cars back in high school for a large detailing company and they liked to use those spray-on dyes. i think they work just ok on some cloth materials and worse on anything else. it ends up leaving carpet feeling crusty even if it looks good. what it seems like to me is just paint that sticks to your interior parts rather than a dye.
i would consider using a dye that is mixed with water that you let your item soak in. i dont know much about it myself but i remember helping my dad restore a 54 vette and he needed to dye the seats and thats what he used and they came out looking and feeling brand new.
maybe others have had better luck with the spray on stuff but i dont think its worth using.
Carquest sells SEM fabric and carpet dye. It is is available in aresol, litre or 3.88L It is about $40.00 a litre and can be applied with a cup gun to do the carpet you only need 1/2 a litre. It is better than the Autobaun or other fabric paints I have used. It covers where as the others always bleed through. It can be used on vynle for headliners also.