An observation that I have not seen discussed: On my 1957 Automatic, I noticed a hairline crack in the inside corner of the right rear engine tab near the bolt hole for the where the engine bolts down to the motor mount plate. It seems like this might be a common problem. When the bracket is missing that bolts the head stud up to the frame, (like mine was), the engine is being forced upwards when the kickstarter is used. And with a missing top-of-engine bracket, the aluminum case becomes the weak point and cracks as a result.
Just welding the cracked case won't fix the problem. The top bracket on the engine head was there for a reason - to hold the engine down to the frame. Good design after all.