Re: A step-thru china girl. Almost.
Maybe I'm mising something in the photos but if not I'm a little concerned about this design. Your reinforcements don't address the problem that all of the weight/stress is concentrated on the down tube to bottom bracket joint.
View the bike from the side then imagine a downward force being applied to the center of the frame. It becomes apparent that the apex of that force will be that weld where the down tube meets the bottom bracket.
Yes, the engine spans that apex but I'm not comfortable with using the engine as a structural member.
Just offering a little advice, not putting you down, sir.
Age and Treachery Will Always Triumph
Over Youth and Skill & "Charlie Don't Ride"