If you have a look closely under the seat you will see it does kick up, it has to to allow the fender to follow the same shape as the rear tyre iykwim

I think your bum looks a little saggy in those overalls ...
But on a positive ,, She is coming along nicely.. For a man with only a hacksaw !
Whats the story on the Underslung battery box , Are you selling ,,
or could you draw it with measurements ?..
I've seen that cheers I prefers it standing up, you can get a kit to do from the USA for 400 dollars plus the usual
I am happy with my one , the whole emphasis about my project is not to buy a load of new bits and try a do it my self. I really don't want a gleaming polished powered coated ornament.
I've been there and done that many times