Hello all- first post from me

I have inherited my son's 1985 4x4 truck. It was (is?) a 'custom' build in which I have very little faith (ie the wank who built it didn't put bolts through the back cab mounts so it hammered itself off, ripped out the front pair, tore the inner fenders off the firewall ... just as an example)

my issue is with the steering wheel being 90 degrees off (turned right) when driving straight ahead. I have no idea which of many possibilities above-noted wank may have done wrong. At straight ahead, Pitman arm looks +- centered between stops, could be upper or lower shaft spline, could be wheel itself not on the correct spline, could be ???

So my question is, what to check in what order

thanks much