"any advice on an antenna if i do mount to the spare rack?"
Welll.., CB radios & antennas are a whole 'nuther science..! I've done many & it seems no two are alike.
The antenna needs to be "tuned" with an SWR meter. Sounds complicated but not really.
Basically, you need a radio, a good antenna & a ground-plane (usually the metal roof).
Most antenna mounts are interchangeable as the coax is like a TV cable.
Many folks mount to the tire rack. It's protected there & usually works fine, as long as it's well grounded.
Antennas are interchangeable as well. That's where a two way radio shop comes in handy.
He can try several types of antenna (and test with the SWR) to get the best match.
Having said that, I've mounted a radio & antenna on rigs.., took off with our group out in the desert,
& they worked fine... no testing or tuning. Sometimes you just get lucky.
My friend broke/lost his antenna out on the trail.., I found & stuck a coat-hangar in the hole.
It worked the rest of that day.
PS I moved you to the Bronco II Q&A slot.