Torsion bar won’t hit header, header will be hitting bar as it is the non-stock part which moves as engine rocks on its mounts when under load.
The difference between 1” and .870” bar is half the diameter increase which in this case is 0.065”… In other words the side of the bar coming close to a header pipe would move only 0.065” closer with 1” bar to that pipe. 0.065” = 1/16” which ain’t a lot.
One possible solution would be to shim engine higher at one of its mounts, or change the shape of the offending pipe with a little tap-tap hammer action without damaging finish if possible. A third would be to install a chain tying block to frame on driver’s side limiting engine movement under hard acceleration. Without seeing where the interference occurs it is impossible to help much from here.
