Watch that top of the head tube sides brazing Abu, my frame wih twin top tubes failed there .

there is leverage from the front wheel that the similar joint at the top of the seat tube never sees..

I had a Irish welder repair the frame crack and add a gusset behind the head tube in the first months of a Bike tour..

the single top tube mitered directly into the back top of the had tube has a solid record of a long time durability

as would a Mixte lug where the tubes converge behind the head tube , rather than remain Parallel.