Here are photos I took of someone's more professionally made two wheel dollie: oak, and better design - I cobbled mine together as I went, working on memory of having seen one once. I built the box, then added 2 x 4s to the bottom, I think three, screwing each to the last with 3" phillips screws - power screwdriver. Makes it easy to disassemble and redo, which I needed to do in order to adjust the balance point. Mine will balance either direction, tail down or keyboard down.
I have two, one large for doubles and a small for singles. I move a single for rentals many times a year, solo. The dollie is wonderful, as it will walk up steps of curbs if needed, and I can tilt to upend (keyboard down) in an elevator, should that be necessary. I generally balance the stand on top of the instrument, to save an extra trip. Drive it up to the van to load tail first, remove the straps, slide the instrument in a ways, tilt back onto its bottom, slide the rest of the way. Reverse for unloading.
The handle in the photo is a nice touch, but would get in the way of upending.
Regards,
Fred Sturm
"Travel is fatal to prejudice, bigotry, and narrow-mindedness." Twain