You would be amazed at what can be accomplished on a good frame straightening machine.
I've straightened more than a few front clips on stock cars that have hit the wall at 80 mph.
Yep...sometimes metal is deformed past an acceptable level...but you just cut that out and replace that section from a scrap clip.
Your frame is full of locator holes that are put there for the frame guy to use to make sure all is square and level.
On your full frame truck...I believe 1/4" out of whack is still the accepted limit.
It's all very easy to measure up on a proper frame machine.
A badly twisted up frame can be made as close to perfect as time will allow.
A factory Icar type manual will have all the measurements that have to be made at the reference points in each model of car or truck.
And yes...the hi alloy frames can be welded.
Most body shops don't have guys who are qualified to weld the stuff so often the cars/trucks are written off.
I have tools I don't even know I own...