believe it or not, I recently run a 390 on a harbor freight furniture dolly. the $18 one with the 4 casters. I used a piece of 4x4 under the front to keep the pulley clear & that was it. I use these to move engines around & they seemed real stable on them. Put a bell & starter on it hot wired a conventional dist. & just sat the radiator in front of it with a box fan. didn't use the water pump fan just in case it fell over. The most it shook was right when it fired, but after that was real smooth. My neighbor stuck around to watch & call 911. Keep a fire extinguisher around, just in case. I shoulda made a video of it.
Back in the 60's when I was 16 I had picked up a 241 Dodge Red Ram Hemi. Don't remember what I used to support the rear of the engine but I used an old 50's chrome kitchen chair frame to support the front. No rad, little coolant and no exhaust I fired it up and of course I reved the piss out of it. It's a wonder the thing just didn't roll off my "stand" down the driveway but it stayed there. My Mom was worried about the neighbors complaining about the loud exhaust but when my old man came home (he was a mechanic) he made me disassemble it and threatened me with bodily harm if I fired it up again.