I purchased an old chiefs SUV from a fire department. When I installed my mobile in the vehicle I had a magnetic mount antenna. Well I'm am upgrading my radio and antenna. I have a one inch hole in my roof from when the fd had it. I did drop the headliner and found the old coax cable with a nmo mount its 3/4" . How did they pull that off? I want to use that existing hole. What options do I have? Thanks.