I have no doubt that a 727 can be built to do the job, but at what cost?

There is a pretty signigifent different difference between a high power motor abusing a trans for 7-12 seconds, or rock crawling at very slow speeds and a 6 mile 6% uphill grade pulling 20,000 lbs.
Ask Rhinodart how those 727s and their derivatives hold up dragging heavy loads across the country. Gene