Thank you Blackhawk--great information! I found a post by Dean on the second link which provided another link to diagrams and procedures for replacing the cups: http://macc.chevelles.net/dash_repair.pdf
I'm now considering a lower priced temporary fix with a modern radio which fits in the currently configured dash (no cups) and new speakers. From previous postings, it appears that finding replacement dash speakers that fit (particularly on the driver's side) is a challenge. I'm considering the 3.5" R-352N Retrofit Speaker or the Kicker 43DSC3504 ( Any suggestions for these or rear speakers which I think would be 6" X 9?"