Everything on my 260z is original, but the speakers sound bad. Looking at replacing but not sure what size I need. Also, went to local radio shop, and since they haven't seen many old Z cars, they don't know either. Also, they are concerned about breaking/cracking the interior panels to get to the speakers. The location of speakers are the ones directly above strut housing. I think speakers are 4" but not sure. Also, can anybody tell me if an aftermarket radio kit is available for a 260? Thanks!

Found this link.....and I believe you are right about them being 4".

http://www.carspeakerbrackets.com/

You will not find any speakers (OEM speakers that is) above the strut housings (towers) on a 240 or 260Z. Any perforations in the interior panels in that area are for the fresh air vents that are part of the "Z" emblems on the exterior.

OEM speaker location is low on the side panel at the rear of the side panel, and the OEM speaker diameter is approximately 5" (the exact size of this OEM speaker is very difficult to find now days. I suspect the brackets offered in the above posted link use a commonly available substitute size speaker.

With a little filing of the plastic console frame you can fit a DIN style radio in your dash. The factory speakers will always sound crappy because there isn't a bass enclosure sealing the rear of the speakers. I know MSA sells a rear panel kit that fits 6x9 speakers or you will likely have to use surface mounted enclosures.

I realize that this is an older thread but in case anyone with a 260z comes looking for answers they can find them. The speaker size that fits best is a 5 1/4" You dont need to use the original speaker brackets, you can simply screw in a new speaker using the original screw holes. I would redo all speaker cable though, if you dont it could cost you a blown set. Good luck.