Passenger side, just inside the cowl. There's a bunch of foam up in there but it's easy to poke through. Just duct tape your wire to a coat hanger, and play fisherman. That'll get you power right off the battery.
You will need to know if your antenna is too short or too long. Adjust it all the way to the long end, then see what your SWR is. The try it at the short end, and see what your SWR is. Also, did you try with the "extra" ground disconnected?