Model Ones are 3.5 x 2.125 in., so slightly less square than humbuckers. IIRC, humbuckers are about 2.75 x 1.5 in.
Hard to tell which these are from the photo, but a Model One has no mounting tabs on the sides. The cavity is routed for tabs, and pics I've seen of a Model G show that it has standard humbucker tabs.
OTOH, I can't recall seeing a black model G before.