I missed your question on the rear shelf with single speaker, mine has this also. RPO U80 optional rear speaker was available with AM pushbutton radio, front or rear antenna, and installed on the passenger side of the rear shelf at an added cost of $12.50. The cover measures 9 and 3/8" X 5 and 3/8" and is black with very small holes covering the entire surface, held down with four chrome screws. As far as the shelf goes, I'm not sure who makes the best repop part and haven't seen any good looking originals for sale in quite a while.
I would use all original parts as long as they are usable, but that's your call. I like to keep mine as original as possible.
Hope this helps and good luck!