Thanks for all the advise guys. Decided the JCR mount wasn't the best option after your responses.
Drove to Ham Radio Outlet and bought a Comet SSB5 NMO antenna and Comet RS-730 lip mount with cable. The RS-730 can be rotated from horizontal mounting to vertical, and will attach to any lip on...
I have a recently purchased 2001 XJ Sport, and a recently purchased Kenwood ™-281A 2M mobile txcvr. My Amatuer Radio license is also a recent acquisition.
I've spent some time looking at antenna mounting options, and am leaning towards the CB antenna mount from JCROffroad. Shown here...