Not sure which crane is being discussed above, but the craned I built performed flawlessly in pulling the engine. The main cross beam is 2"x3"x1/8" tube steel and spans 6'-10". The base spans 4'-6".
Incidentally, I have an engineering degree (but not a practicing engineer) and I am struggling to understand where there are moment forces (other than insignificant) in my design. Sure, the braces are there to handle the insignificant moment forces at the otherwise pinned connections. But, the forces are balanced.
