That mount is a CB mount with 3/8-24 mount for an antenna like a firestick. You've got really 2 options with ham mobile antennas, an NMO base or a UHF base (SO239). I think you could get an adapter to go from 3/8 to UHF. Associated Radio sells a mount just like that, except unfortunately the hole pattern is rotated 90° for your holes you already have. They might have what you'd need to get adapted to UHF or NMO. I'd recommend a trip by Associated, he'll be able to get you set up with what you need. If you make a custom bracket with a 3/4" hole in the top you could go NMO pretty easy.
As for antenna, I just switched to the Comet SS680SBNMO (I use NMO mounts) from an SBB1. SBB1 was nice and compact, but sucked for any kind of distance. With the 680 my Tx/Rx is significantly better. Has a spring loaded base and isn't crazy tall, so it's a good compromise for off road. Jack and Rob both run them as well.
For radios, I'd reccomend a dual band. I ran a 2M only Yaesu 2900 in my crawler for years, great radio and built like a brick but isn't going to work on the Rubicon's 70cm repeater (or at all for that matter, it's dead), so I'm looking for an alternative.
Jack and Kelly just got the Yaesu FTM6000R, which is a dual band rig. It doesn't have dual receive, but I believe it has dual watch so that is probably good enough for what you need. For $10 more you can get the Icom 2730 which has dual receive and can do crossband repeat.
Another $150 on top of that and you can get a Yaesu FTM3000 that has Fusion digital and APRS, or for a little bit more you might find a used FTM4000 that adds touchscreen.
All those radios are top notch. My next radio is a potential crap shoot. But it's less coin and small (but no detachable face like the ones above). I just bought a Retevis RT95. For a $100 Chinese radio, the menus are easy to use, it's easy to program from the face, and it also came with a programming cable. Dual band with dual watch. Scanning is painfully slow, and there is no dedicated volume knob. I bought it for an APRS/comms manpack for Rubicon, and have gotten great Tx/Rx of APRS packets as well as good audio reports from repeaters. Seems to be a pretty solid little performer. Also only 25w, so less powerful than above radios. For your main/only radio, I wouldn't rely on it, but figured I'd throw it out there to balance out the pile of cash I suggested above.