Yep Matt - they tip. I found that I could actually hold a 351W SB Ford from tipping over after it started. Couldn't straighten my back out for a week afterwards - but the engine never hit the ground.
Those mods are about what needs to be done - you but might consider a ride to Albany for the $60 HF 1000# heavy duty version
instead of spending time on cobbling up the 750# light duty stand.