Radio Antenna Replacement Question

[tucsonjwt]

My 83 C20 has an aftermarket antenna mounted on the passenger side fender.
The cable for the antenna is routed into the engine compartment, under the cowl screen, then down under the dash.
I can't see how to remove the antenna mounting base on the fender - there is no obvious access to grab the underside of the mounting bracket. Must the fender be removed just to replace the antenna? I don't know if the 83s had a fender mounted or "in the windshield" antenna from the factory.
Also, what would be a proper antenna to replace it and where can I get it? I like the new style screw off antennas, but I don't know if they are compatible with the cable connection I currently have.
Thanks.