Regarding the Sprinter, was there a reason why the full-size Transit wouldn't work for you?
AFAIK, you can actually get one of those in a diesel, as in they're on dealer lots.
Well first, having had the opportunity to service both of these models on numerous occasions, the Sprinter is a superior vehicle in pretty much every way. Better built, with better attention to fitment of the components, easier to service, sturdier suspension and steering, FAR better brakes, and more room inside.
All Sprinters (sold here currently) are diesels, so it is not an extra cost option to get. Ford wants over $7k for the diesel engine option. The low roof Transit is not tall enough, so I have to step up to the medium roof. And the short wheelbase Transit is shorter than the standard wheelbase Sprinter, so I have to step up to the longer wheelbase Transit, which also means stepping up to the heavier GVWR (so instead of a "250" it becomes a "350").
The diesel in the Transit has an extra cylinder I do not need. But I would since I'd now be asking it to move a small schoolbus. The Transit's standard electrical system is not sufficient for the wheelchair lift requirements, so that requires an extra cost upfit. Sprinter's standard alternator and battery combo meets the lift company's requirements.
So, I can buy a $41k Sprinter that is large enough, more durable, more reliable, and more efficient... or I can buy a $48k Transit that is larger than I really need.
Oh, and there are NOT any Transits on any lots like I want. It would have to be ordered and custom built. And then I am back to square one.
If I cannot get confirmation on a Sprinter build by Jan 1, I will be shopping for a slightly used one that almost certainly will not be equipped the way I want it, but I really need something larger.