I checked out the Bombay handlebar and I am pretty sure the tach housing will run into the shroud. However, I have one so I am going to mount it just to check it out. My current thinking is I would like to have the option to run the shroud and I want a tach too.
Check out the 2006 P&A book on Pg. 645 item F (For some reason it doesn't come up on the H-D website 69277-05)...I was thinking it *might* work if you remove the FXDWG3 chrome trim underneath the shroud. I think this is the same mount that comes on the 2006 SE Fat Boy. If your dealer has one of those, you might be able to measure to be sure. Pretty expensive at $250 and that is just the top clamp. You still need the housing and tach. Notice that the part of the tach mount is machined into the top clamp to save space. If it works, it would be an awfully "clean" solution. Either way, I think you are going to lose your chrome trim piece though...
If you try it, make sure to post back with pics. I'll do the same with my investigation with the Bombay.
Kevin