1967 Barracuda rallye dash instrument panel housing with ac

Difference in speedo is how the cable attaches ( back view ). 67 uses a collector nut similar to transmission attach method so you should see threads. 68 and later use a plastic clip on this end of the cable, so no threads , just a shoulder for the clip to sit behind.
You'll find that housings and bezels and climate controllers are different. Use whatever gauges you want in 67 housing with 67 bezel in a 67 dash. If my memory serves... there's a one wire difference in the 67 and 68 up a/c controllers also. I think other owners have found a solution for that. Cross that bridge if and when.