JB wrote "No "internal" reason for Superman to be as muscular as Cap, really."

*****

Maybe this kind of "Classic" cover had an influence on myself and led me to think Supes is as muscular as Captain Marvel ... but I agree with the fact that having a super strength does not imply to be very muscular .

Concerning your latest question, John, "So where did Superman's big muscles come from? ", I think we could open a tread about it.

We could imagine Supes has the "standard" Kryptonian morphology and that Kryptonians are all built like a tank. But we have already encountered others Kryptonians not so muscular. So maybe Clark's body had to increase his muscular density so that he can store all that solar energy. What do you think (in another tread, I guess...)

Shouldn't the part of the cape that I've circled in the image below be WHITE instead of YELLOW?  There's no "border" there -- that's where the cape drapes over the neck cord . . . so the yellow edge border shouldn't carry through to this part of the cape:

Or am I mistaken on this?  Just finished painting my custom JLU Captain Marvel and the edging on the cape was a PITA, so I'm painfully aware of how I think it should look.

[EDITED FOR TYPO]

Not the best quality picture but here's Booster Gold.