Reply to "2 or four bolts main caps, is it so impotant?"

When cylinder walls fail they crack through to the water jacket, and sometimes a big chunk of cylinder wall actually breaks away from the cylinder, leaving a big window exposing the water jacket. You can't use a dry cylinder liner to repair a cylinder damaged to this extent. There are such things as wet cylinder liners, but I have no experience with them, I don't know if they're worth a damn.

An engine limited to 6200 rpm, 8.0:1 dynamic compression, can get by with slipper skirt type pistons. But if a person wants to rev the engine higher and takes the cylinder wall weakness seriously they should do the following:

• limit engine speed to 7200 rpm
  
• limit "dynamic compression" to no more than 8.0:1
  
• install round skirt pistons
  
• dynamically balance the reciprocating assembly
  
• consider installation of longer (351W) connecting rods (rod length to stroke ratio = 1.7:1)
  
• Limit horsepower to ~450 BHP (?)

That's more or less what De Tomaso did to get the "early" group 4 race engines, based on the production block, to survive racing in the world endurance racing series (I don't know if they used longer rods, but their dynamic compression was closer to 7.6:1).

Most street engines are never stressed by operating a lengthy period of time at wide open throttle, even on the dyno they're never wound -out for more than a few minutes; so they can get away with higher compression, higher horsepower ... until the day the owner decides to take it to the track or wind it out across a empty desert road. Operating WFO means the engine is operating at maximum volumetric efficiency, and cylinder pressures are at their highest level. This is what stresses the cylinder walls.