If the truss can be loaded with enough weight and not deflect (or explode), we'll have good reason to continue production. Driving the truck to the nearest scrap yard to borrow their scale, the truck sits at a healthy 5340 pounds. Balancing the front wheels atop one truss will load it about 3000 pounds - more than enough weight.
The whole thing became quite the event. Fortunately so, as our street-friend was there to keep the two-and-a-half ton truck from falling. After several more attempts to secure the truss in place - and keep the locals at bay - we retired without a successful test. I'll revisit this in the future using car jacks and lowering the wheels onto the truss instead.
In the meantime, I've been lucky enough to have been in touch with a structural engineer who is looking over the current design detailed below, pro bono. Within an hour of sending Jon the drawing, he had worked through all the calculations. This must be why engineers get impatient with architects.
All of the members work out fine, but the connections require something like 26 nails each to hold - which is far too much. This doesn't include include the strength of the construction adhesive, so after figuring that in, we may be okay.