What Hambleite said.
Nice boat, good price, and will go well with the 55 on.
I had a non-GT Force 4(with the flat front) that I dropped a 55 on and it went like stink, just a little unstable at WOT.
Just reread your post, at 16.5 feet I think it's too long for a Force 4 GT, probably a Force 5.
The F4GT was a F4 with a pointy Bow, and that wouldn't account for an extra 4 feet.
The length of the area behind the rear seats is far too long for a Force 4
Have a look in my gallery for some old F4 pics to see the difference.