I ended up using a VDO/Continental unit that I've used in European cars before. Nothing fancy, but has bluetooth and front aux in. I added a NISSAN sticker I made. I chose the model with blue illumination because that's what the original Blose unit had.
https://www.amazon.com/dp/B091Y3L22L
I used this wiring harness. My car had already been modified to bypass the Blose amps. Had to swap the yellow and red wires on one plug, and had to cut one wire to ground the unit properly.
https://www.amazon.com/dp/B0B7P3WMLM
I also replaced the weird center speaker with a cubbie, and put two lighter sockets in that. Kinda a reach to plug something in, but will be convenient to have.
The cupholder is just a little plastic panel from ebay that replaces the ashtray. You're supposed to glue it in place, but I added a single hole and used a #10 x 1.25" screw from the hardware store to hold it in place, seems to work fine.
https://www.ebay.com/itm/266688087680
A few pics.
Vintage look radio in 300zx by centerpunch, on Flickr
VDO/Continental radio in 300ZX by centerpunch, on Flickr
300zx cupholder installed by centerpunch, on Flickr
300zx ebay cup holder by centerpunch, on Flickr

