When I was involved in building dump truck beds for Cat, we just used D1.1 for NDE requirements per material group. But, we had an in-house design that was approved by Caterpillar and using their materials.
Problem with Cat is that they have their own steels custom made with Proprietary recipes. Our QC library must have had about 20 volumes (At around a thousand pages each) of Cat steel material specs. Some steels are T1, and A36 that were just rebranded with a Cat number, but most had some pretty exotic formulas.
That most likely didn't help too much, but if you have a particular component to repair or build, my advice would be to contact Cat and see if they will give you their procedures, consumables, specs, etc.
I'm reasonably sure Cat uses D14.3 for it's equipment fabrication and repair. While there are many connections with D1.1 you will find many variations within D14 codes. And D14.3 should be the code applicable to the general equipment manufactured by Cat.
Have a Great Day, Brent