Had a chain break on a small pinto engine when I was in high school and it scared the heck out of me. The engine fell back into the engine compartment, fortunately it fell directly back onto the mounts so nothing got damaged. From that point on I learned that spending a couple more dollars on grade 8 hardware, and the single bolt where it attaches to the cherry picker is always bullet proof.
Except for the main pivot bolt on the head of the cherry picker their should be at least two chains connected to the motor so in the event one blows the other is there to at least hold it from falling. I just pulled my motor this weekend and it was the first time I used one of those load levelers. they really keep the load from shifting or hanging at crazy angles and stressing out the rigging.
What ever you do don't give up on your build. Frustrating things happen all the time it is just part of the stories you get to tell when you are at the truck show with your newly completed project.
