Is this frame welding/modification normal on a 1987 Chinook GMC (Vandura 3500 dually)?

[Arne Loonen]

Hi all,
We’re inspecting our 1987 Chinook GMC on a Vandura 3500 dually chassis and came across something questionable on the frame (see photos).
There are steel angle brackets welded onto both frame rails (left and right, in similar positions). The weld quality looks rough — inconsistent beads and not fully continuous — which makes it seem like a non-factory modification rather than OEM work.
In the same area, some of the hard lines (likely brake and/or fuel lines) appear to have been cut and transitioned into flexible hoses.
Structurally, everything feels solid: no movement, no play, and no visible cracking around the welds. It looks like this has been in place for a long time and the vehicle has been driven like this without obvious issues. Driving behavior, braking, and alignment all seem normal.
Has anyone seen similar reinforcements or repairs on these G30/3500 chassis or Chinook conversions?
Are there known weak points in this area that could explain this type of reinforcement?
Or is this almost certainly a previous owner repair/modification?
Any technical insight would be greatly appreciated.
Thanks in advance!