Antenna arrived today. Took said antenna and radio, a Sirio Performer 5000 and Uniden 78 Elite combo to my installer and they showed me how it will not work in the roof because I ordered the wrong base and without the coax with right-angle connector.
After much discussion I decided to have them install the Performer on the left edge of the hood, a simple install until I can assemble the right mount and so on for the roof mount. This happens tomorrow.
The good news is I will be able to do it right with proper parts and support for the roof too. I talked with my head mechanic and he described taking out the headliner, a time consuming task I might do myself later on in our shop.
General reading led me to an article on ground planes and how to achieve that in a vehicle. It occurred to me I might be able to measure SWR improvements after the radio is installed, as I ground the hood and hatch to the body, even grounding the muffler system for whatever slight improvements that may glean. Anyway whatever comments you guys have would be interesting.