Since you seem unwilling to accept facts, try this: do you really think the weak link in this chain is the bolt? How strong do you think the cast iron is that the bolt is threaded into? If you were to keep adding weight until something failed, it would be the block. That much you can bet on. Also, shear strength would only be a factor if the center of gravity (threfore the primary forces on the bolt) were at the point where the stand meets the block. Instead, the real center of gravity would likely be somewhere near the center of the cam, since the majority of the weight lies above the crankshaft of any V8 engine. Think of it as holding a baseball bat out at arms length by only the handle, is the handle pushing down or is the tip furthest from you pulling down? That is why tensile strength is the acting force, NOT shear strength. You can argue with me all day long, but the fact is, you have no real proof that grade 5 bolts are not enough to hold ANY passenger car engine, now do you?
Damn why not just go ahead and use some 1/4 inch bolts? I'll bet their grade specs exceed the weight of a fully dressed motor too? 
