Rick, sorry for my late reaction. Thanks for pointing out these differences. To add to the discussion, I have posted the pictures that are keeping me busy, below:
Rampant Rivet's C15:
Than Jordan Baker's C15A:"
And Plushy's F15:
RR's C15 frame seems to be different from other Chev frames in a way that the bar from left to right under the seats, seems to placed far more to the front than with a C15A, C60 etc. Also the bar on the right hand of the engine seems to be missing. This would also mean the floorboards on a C15 are different from the other Chev's(?)
Alex