Most that Larry describes I would consider underpowered power-plants for the blower size, a mistake I feel WAY too many TM manufacturers make.
Water or air cooled makes a huge difference in the equation as well not only for power and torque, but for heat producing capabilities.
My ideal slide-in for single wand:
59 turned by a straight or slant six motor in a large box truck with a big footprint to eliminate restrictive bends as much as humanly possible. I'd happily deal with less floor space for more efficient power. I'd just utilize more shelves and overhead racks. BTW my box truck would be tall enough to easily stand in too.
I'd want non-restrictive plumbing, simple wiring, few electronic safeguards, a carbureted motor, direct drive, simple, non-restrictive filtration, 200 gal stainless waste (because i don't filter, I don't like APO's), soft water, dual hx with an optional propane boost. 2 electric vac hose reels - one for 2", one for 2.5".
Oh, and the truck would have a HOOD!
Take care,
Lisa