Not a very big problem either, as a less-wide bakbrommer will tumble over easilly in a corner, i wonder if you will experience the lack of grip before that happens... (it's not lack of traction)
But it's best if you apply the right steering geometry right away.
If you would like to make a very light bakbrommer, i would think of welding something like Irmin has made, but smaller and less compicated.
Less complicated, because the complexity makes it a bit heavy.
Irmin's bakMOTOR (it is officially a motorcycle) has a 600cc mono-cilinder if i remember correctly.
It is not that complicated in fact. you can make a nice autocad drawing. perhaps even 3D if you feel like it (just lines are well enaugh for this job)
Anyway, I wish you best with your project! Will you show pictures of what excellent madness you fabricated?
B.