[Ron Ramirez]

Am I correct in dating this chassis as a 1935?

Nope, it is a 1936 model.

Chronologically speaking, the 660 came out in May-June 1935 with the rest of the then-new 1936 Philco line. The 665 would have come out in January 1936 as a replacement for the 660.

Just like a new line of automobiles used to be introduced in September of the previous calendar year, new radios came out in June of the preceding calendar year with "mid-season" replacements/additions in January.