Every shop I know of pulls the cab.. It's easier. Not me however. Beyond my capabilities.
What I find amazing (with the cab off and I've seen more than one), is how corroded the engines are...
That is a non issue with my OBS. When I got the truck new, I lined the openings in the wheel wells with rubber sheet. Keeps the stuff off the engine.
I have no emissions hardware on mine at all. I even eliminated the crankcase breather back into the turbo inlet, added a road draft tube. Replaced the turbo pedestal with a delete pedestal as well. Along the way I added lockers front and rear and roller bearings in all the suspension pivots.
Finally, I stripped the horrible clear coat off the aluminum wheels and polished them.