Adler
I have a couple of books, unfortunately still packed in storage, that have quite a bit of info on this aircraft. Reminded me a lot of the Westland Whirlwind, similarly laid out. Similar performance, too, but that of the Whirlwind was little better. I don't remember why this model was never selected for mass production, but its design became the basis from which the later F7F Tigercat was developed from, if I remember right.
The Grumman fighter line up went something like this:
F2F & F3F - 1 engine biplane fighters
F4F - Wildcat
F5F - the 2 engine mystery plane below
F6F - Hellcat
F7F - 2 engine Tigercat
F8F - Bearcat
F9F - post ww2 jet, Panther I think
Not sure of their fighter aircraft before or after these.