Well now, you could say it is screwed as is and there is nothing to loose by attempting to straighten it.
Bends in tube are always frowned upon by some, yet bent fork legs are regularly re aligned by established specialists, so it can be done.
With the bushes removed, if you get that far, a mandrel and levels will establish if a problem actually exists, with the bushes still in place, how does it look within the frame? At the end of the day a few mm will make little difference on a bike used as most old bikes are ridden. Take the rear spindle as a datum, not the fork end forgings, see how that compares to the cross tube.
A hydraulic press and a few supports will flex the trailing arms into line, a bent arm can also be coaxed back into alignment. If the arms are straight, it's just a twist in the cross tube.
Swarfy.
PS Just read your first post. Registered with a "Scottish Number Plate" could be age related number allocated to a fine assembly of unrelated bits, so unless it's kosher, expect every malady known to the Forum.