John, I agree that the 665 and 2065 are reminiscent of the Baldwin / CNJ P47 Pacific because of the Elesco-type feedwater heater, tall driving wheels, and compact length. But the rest of the body shell is the same as the 685 / 2055, which is patterned after a Santa Fe 3465-class Hudson. These often came with a rectangular tender, which is also similar to tenders used by the Santa Fe.
The larger Hudsons (646, 2046, 2056) use the same boiler casting as the 726 and 736 Berkshires, but with six large wheels instead of eight smaller ones. In this sense, they are a reversion to the configuration of the parent model 226E, except with a more prototypical 4-wheel front truck. They could be thought of as a traditional-sized version of the NYC Hudson (as opposed to the 773, which was a full 1:48 scale size.) These are great runners, but visually they have a lot of overhang on O27 track.
The smaller 2-6-4 models beginning with the 2036 evolved from the pre- and postwar 1666. But multiple changes to the boiler and pilot castings beginning in 1947 gave it a very modern appearance. It's not a faithful model of any one loco, but I love the styling! The bulky radiators on the pilot deck and large dome bristling with sanding lines remind me a lot of the of C&O Kanawha, and even the P&LE A2 Berkshires. I always thought of these as a type of O27 Berkshire having six driving wheels instead of four. (Full-sized Berks like the 726 could not run on O27 track.)
You didn't mention the 2-4-2 "Scout" types, beginning with the 1684 and continuing right through the present day! Again, no specific prototype, but I always thought these resembled the NYC H-5 Mikado (which in real life was a 2-8-2.) The Mikado was a ubquitous freight hauler, used on all branch lines after WWI. That's how I used my 2-4-2s (and we had a LOT of them), so I guess it makes sense to me!