I don't know the 23B coupler height, but as a last resort a call to Jayco should get the info you need.
Just a heads-up on the Reese HP Dual Cam ...........;
When you go to mount the Reese HP 'frame plate' to the HTT's A-frame, check your location dimensions at least twice and insure that there aren't any gaps between the frame plate surfaces and the A-frame surfaces before drilling (large C-clamp works great). Maintaining the specified torque specs for the thread-forming screws @ the frame plate is important (don't guess).
One thing that many folks overlook is the proper chain assembly/mounting of the hanger bracket to the cam arm, please note:
New HP Version:
Older HP Version:
Enjoy the new HTT