Interesting, I have only seen block crack on 5.0. Don't know how bad the problem is on the OHC motors. I would expect that unless your running a lot of boost, NOS and doing serious drag racing this is a waste. If you are doing that type of work, spend some extra money and get a solid block if available, it not only won't crack, but will make more power due to a more rigid design. I have seen only a few split blocks and they were from NOS/Blower/Slicks applications. I would guess the small pins are only in shear and keep the block from pulling apart. Roll pins are pretty strong in shear and that is about all this looks to do. Hey might work great, but I'll bet more of a pain then its worth. If your making a lot of power and your using a 2 bolt or other weak late model block don't expect this to solve all your problems. Now if class does not allow aftermarket blocks, I guess you have a reason to give it a try. 2 Cents

This is a really good question. I often wondered the same thing. The claims made by Horse Power Sales, the company that makes the valley girdle, seem a little optimistic, so I spoke to a few engine builders to get their opinion. Please note, that these are the opinions of one guy at each company and is not reflective of the company's official position on the valley girdle.
1) DSS Racing - "I would think the intake manifold would create enough bracing for the top of the motor to not justify the cost. The real vibration is at the crank, so a main cap girdle is where you want to put your focus.
2) Coast High Performance - "A guy here runs a CHP 347 Ford with a main stud girdle and a valley girdle and is making 630 rwhp... So it probably is doing something good."
3) Bennett Racing - "This is not something we've ever used, but whatever machining it would take to install it would be better spent on a Dart or other 4-bolt block. That said, I guess a valley girdle couldn't hurt."

This is a reply in regards to your questions about Valley Girdle Pro.

1.) Shear strength on each pin: 10,500.

2.) Intake Manifolds actually wedge the engine apart.

When an engine fires, it fires from opposing sides - thus the start of block flex. The VG Pro will prevent the twisting of an engine, therefore avoiding cylinder wall distortion and piston bore distortion.

Valley Girdle Pro has been on the market now since 2005. Raced and test proven. Valley Girdle Pro has been patented and is now recognized for being in the famous HP2g engine. HP2g is an official Progressive Automotive X PRIZE contender (a viable, super-efficient 100 MPGe technology scheduled to race in September 2009.)