I'm willing to bet the steenbeck can handle it. They're built like tanks. But I'd watch out for any connectors and switches on the back when setting it down. I would have at least two strong people helping with this. I can think of two ways you could do it without damaging the legs:
1) lift it up slightly, have a third person stand where the projector unit is to help, and tip it so the back is facing down before lowering it onto a dolly, keeping the legs completely off the ground the whole time.
2) set up some bracing under the unit (like we did with my 1901, with plastic milk crates -- which are freakishly strong) so that the legs are off the ground by a few inches, then tip it up onto the crates and remove the legs before lifting it on to the dolly.
a good set of appliance moving straps are going to help you a lot. It's kind of amazing how much bulky, awkward weight you can carry on those with relative ease. With two sets of straps and four people, you could probably even get the whole thing lifted up off the ground, and then tip it back in the air, while it's cradled on the straps.
We had a 400lb stainless steel commercial style stove in my apartment, and when it died and we replaced it, the delivery guys who brought the new one, took the old stove out like it was nothing. two guys, one set of appliance straps and a flight of stairs. They barely broke a sweat (and they weren't particularly burly either).
It might also be worth finding out how much some piano movers would cost you for an hour's work since they probably deal with the same problems all the time...