Similar make of horns on the 260Z but they use a centre bolt with right angle bracket mount.
Our 2000 Sports has horns with this style of mount.
I fitted the old horns replated just for originality, but fitted Denso horns for tone.
With the age and plating of the the rusty diapraghm they just never had the right tone again, sounding a bit flat inspite of the tuning,
If you get some old horns you can swap the diapraghms around to play with the tone.
There is also a high and low tone in the pair.
Denso horns- smaller physical size but work great.
https://www.ebay.com.au/itm/CAR-JDM-HORN-DENSO-HORNS-12V-2-PIECES-RIGHT-AND-LEFT-UNIVERSAL-Tone-111-db/222993597649?epid=13010486078&hash=item33eb7444d1:g:r00AAOSwTbVbCZHw