One thing I rarely see mentioned in talking about sheaves (pulleys) and snatch blocks is minimum bend radius of the working line. Each type & diameter of cable, line, rope, whatever you want to call it has a minimum bend radius. Most manufacturer's publish this info. Using a sheave of a smaller radius starts to break down the line itself.
A designer who knows what he or she is doing will set the sheave's diameter such that for the intended maximum load the largest likely cable isn't bent smaller than it's minimum bend radius. Using such a block with a larger than expected line, even though you are still within the maximum load limit of the block, is detrimental to the line itself (& potentially dangerous) because the sheave's diameter is too small.
Other than actually hauling it around, it never hurts to use a sheave of an overly large diameter.
The block Roberto found looks to me like a well thought out project. I'm not sure that it's a production part intended for the military as it looks too much like a prototype part.
