not to be rude, but I already knew that, I'm interested in the physical differences...I've been told that the frame is much heavier on the F2 compared to the F1, making it not-so-great rod material
A lot of the parts on the F2 are subtly different than the F1 parts, such as fenders and running boards. F1s tend to be worth more. Lots of F1 parts are reproduced, but not as many F2 parts, so replacement parts could be harder to find if you're not into making your own patches. A tip for telling an F1 from a F2: The front fenders are split into two halves on both models, top & bottom. The F2 fender openings extend above the top/bottom split line, where the F1 fenders are about flush with the line.
My take is that F2s can be cool, but it'll probably take a bit more work and scrounging. I think they are a bit heavier due to a larger bed and beefier suspension components. I'm not sure about the heavier frame, but I wouldn't be surprised.
I don't think the frame is that much heavier. The F2 was considered a light 3/4. F3 was a HD 3/4 ton. F4 was 1 ton (at least in '48) Box is longer at 8' and wider by about 5" at 54" It has narrower rear fenders as the box has slender tubs inside. Wheel base is 122 vs. 114" I'm running F3 front fenders on my F1 with 16" wheels and I've grown to prefer that look......... Check out the 48-60 forum at Ford Truck Enthusiasts. A couple of the guys there are making ex-cabs and at least one has shortened a long frame for a short box. Brakes are different as is the rear end, but F2 has 3" axle tubes which makes substituting a 9" rear easier. Steering gearbox is the same gemmer 3 as in the F1.