Originally posted by MarkO:
Correct me if I'm wrong but non-interference engines have spaces or shaping in the top of the piston to accomodate the valves in the event of a catastrophic fail.


You are wrong to use that as a point of reference.
The valve reliefs cut into the pistons are only done on engines that require it so the 2 parts do not meet while moving. It still can be an interference or non-interference engine.
For instance the 3L Duratec has valve reliefs cut in the pistons due to the close tolerances and it's an interference engine.

2000 SVT #674 13.47 @ 102 - All Motor! It was not broke; Yet I fixed it anyway.