If you look you can see the chassis is actually mounted to a board that slides into the cabinet, I think the CBS RX90 sets had the same arrangement.
I don't have to much info yet on how long the set was in use, after it arrives I'll contact him again for the particulars. I was hoping there was some original paper with it, but no such luck.
The speaker grille layout is interesting, I finally found some info on it on Tom Genova's site (
http://www.tvhistory.tv/1955-Philco-Brochure1.jpg).
Philco called it "Phonorama Acoustic Lens System"
Looks like it was used on their high end sets for a couple of years.
Chuck