Removing the bulkhead
To make it walk-through from cab to living quarters.
Starting point, after removing the LPG tanks:
The bulkhead panel & frame had been hacked about with a grinder to squeeze the LPG tanks in:
Many scrivets removed, old rockwool insulation removed, frame exposed:
Many more scrivets removed, front panel cut with Fein tool (awesome bit of kit for this sort of thing):
Frame cut out, two lengths of 50x25x3mm box cut to go in the gap:
The original frame sat on the floor and was bolted through the floor with fairly skinny (M6? M5?) machine screws.
New uprights marked & drilled for all the rivet & scrivet holes to line up plus the seatbelt top mount bolt holes, then dusted over with cold galv / high zinc paint:
New uprights welded carefully in position without setting fire to the rest of the vehicle (but note fire extinguisher just in case!), joined to existing frame wherever it touches. More cold galv on all welds:
Wait, you just said you weren't going to cut big holes in things, but look!
Yeah, we lied. 
Actually, although this looks drastic, the missing section could be easily fabricated & welded back in, and the panel had been butchered by the LPG install anyway.