additionally, another small feature is checking the console itself. Look for the cutout on the lower front half of the console, and check the lower console mounting bracket to see if the guage wiring harness bracket and plug socket are there.
An interesting point was raised on the console bases and wiring harness details in the AIM by Chick during his 68Z build thread over at Team Camaro. The theory is that no '68 consoles had a cutout in the front, nor a console bracket with the harness clip, but that in '69, all brackets had the harness connector clip, and a forward cutout. This is irrespective of the console having gauges or not.
Since that was raised as a possible theory, I have looked at every 68-69 console on eBay, CL and at swap meets, and have never seen a 68 console (off-white plastic, viewed from beneath) with a cutout, nor a 69 (black plastic) without a cutout.