I was looking for a CB antenna when I added a CB and went with a Sierra combo product. (AO-GL12-ANT GL1200 ANTENNA) This antenna fit the right radio mount. It is a folding antenna as well. It requires thier antenna splitter, CP-27F. If I recall there is an adjustment on the splitter and the top part of the antenna is held by a set screw which would allow some up down adjusment. So SWR adjustment should be possible. Note there is a CP-27 splitter but it has a PL-259 connector for the CB lead and will not connect to the Valk CB.
I went with the Yamaha Royal Star Venture CB as it was easier to locate then the Honda CB. Mounted it under the trunk using the HOnda bracket and extended the power lead.
Antenna
http://www.sierra-mc.com/proddetail.asp?prod=AO-GL12-ANTSplitter
http://www.sierra-mc.com/proddetail.asp?prod=SIE-CP-27F