80 series steering box problem

[DesB]

My HZJ80R got sideswiped while parked 😞 by someone who drove off 😞

They hit the front wheel drivers side - gave it a real belt (sufficient that they left bits of their mag wheel on the road and drove off on the rim...)
Strangely, the alignment wasn't too badly affected - if I centred the steering box (equal turns left and right) the front wheels still pointed pretty straight ahead.
Drag links are still straight.  Pitman arm looks fine (though the complex shape makes it hard to know for sure). BUT....

The fundamental problem is that somehow it affected the alignment between steering box and steering wheel, though I can't figure out how that could happen.
When the steering box is centred (equal turns left and right) then the steering wheel is way off centre - about 1/3 turn to the left, so the bottom spoke is under my Right thumb.
When the steering wheel is centred, then of course the wheels point very noticeably right. The steering itself still feels smooth.

I initially (on mechanics advice) just got a wheel alignment - they centred and clamped the steering wheel and got the front wheels pointing where they should, but of course the steering box is then not centred, with the result that I now have just over 2 turns to left lock, and just under 1 1/2 turns right lock, instead of 1 3/4 both ways, so a horrendous turning circle going right.  This gels with the original observation of the steering wheel displaced by 1/3 turn.

My mechanic says the splines on the pitman arm are twisted, but that doesn't explain the fundamental mismatch between steering box and steering wheel, which is there even if there's no pitman arm.
He also said I need a new steering box and pitman arm, which of course should fix everything.  But I can't see how a hit like that could have the effect I've described.

Anyone come across anything like this?

There are splines above the steering box that I think could be adjusted to align box and steering wheel, but I guess *something* in the steering box is damaged and I'm best just to replace it?
Speaking of which, I've priced a 2nd-hand one - the supplier said its from a 100-series with "solid diff" (whatever that means), and should be compatible.  Can anyone confirm if that is true?

DesB

PS I have a copy of all the relevant 25 pages from the workshop manual.