I think this. a 10mm wide 865mm long v-belt. Gates are good.
https://www.ebay.co.uk/itm/321822580433
I did some digging on this a while back, see here --> https://zclub.net/community/index.php?threads/240z-fan-belt-recommendations-please.23469/
I failed to update the thread but I ended up with the DAYCO belt and it fitted my car fine. I bought it from here --> https://www.ebay.co.uk/c/1709436990