Re: A step-thru china girl. Almost.
As a matter of fact I did see the bracket you mention, on the seat tube but I feel it is too low to add any real support when you think about road shock, rider weight, etc. being applied to the frame and the point that will need to withstand that force. Even with that bracket the downward force, or maybe I should say, the rearward presure of the head tube pushing back will impose a lot of force against the down tube/bottom bracket weld joint. In the original configuration, the seconday down tube you removed was there to take some of that force. With it no longer there everything is concentrated on the lower end of the down tube.
Whatever, please be careful and keep a close watch on things. Good luck, sir and let us know how things go.
It would be cool to duplicate that step-through bike you pictured. Neat idea.
Age and Treachery Will Always Triumph
Over Youth and Skill & "Charlie Don't Ride"