Steve, I have the ACR RCL-75 mounted on top of my PH roof. It is not glare free, but part of that is due to the upturned bow. (Should be much less of a problem on a Parker due to the nonskid cuddy roof and the lower bow).
One advantage of PH roof mounting is that it's possible to aim the spotlight farther backwards than 90 degrees withouit blinding the coxswain.
My preferred location would have been at the point of the bowrail (no glare on deck/cuddy roof), but it was going to be a royal pain to run the wiring.
Part of the mounting secret is to mount it as far back on the PH roof as possible....since your radar is mounted aft on an arch, you can go back a little further than I did (need to keep it forward of the interior rib in the roof to conceal the wiring).
Don't throw away either your self-contained or plug-in-the-lighter spotlights...they will still come in handy...