I'd love to see pictures from your conversion. I was working on something similar a while back, but using a cut down headset to join the frame. I had a length of wood inside to give rigidity to the join. It did work alright, though the headset joint worried me as it was maybe only 3 inches in leghth, and I wasn;t convinced.
Unfortunatley, I can braze, but haven;t really got the skill to make something from scratch, so have to rely on something ready made to do the job.