Buy a couple of pieces of square tubing that will slip inside those legs, and move the casters forward beyond the front of the crankshaft at least a few inches. If you're working on a V8, just slide them back until the casters touch the outer tubes. You can either weld a nut on top of the outer tube for a clamp bolt, or cross drill the tubes so the length of the legs is adjustable. Then reposition the spider so the pivot tube is at the canter of mass. Safe is much better than sorry!
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!