CAT 3126, in trucks, were all electronic and HEUI engines, to the best of my knowledge.
There was a 3126 mechanical engine in the Marine industry, that I have seen. (looked more like the old 3116 mechanical engines)
Yes. I have a 3116 standing beside it now and they are almost identical except for the 0.1L / cyl bigger . And 80 hp difference :-(
The Challenger tractors had these too but any I have seen were very high hours .