So, based on your observation of the relative amount of water that has been in #4 to #1, I consulted the engine rebuilder. He loaned me some tools and my chore today is to rule out some low chance possibilities and then pinpoint location of fault:
1 Check Calibration of torque wrench
I'm sure the torque wrench is fine, at least within 3 lbs.
2 Do a compression check. He suggests that it should take a lot of over compression to cause gasket failure so fast (like 500psi) Little chance the small piston size diff is causing this.
Agreed. From what I see I don't believe this is the problem.
3 Pressurize the water system with compressed air. (Do not exceed radiator cap pressure, you could blow coolant pump seal) Pull the glow plugs and turn over. Look for water vapor to lock down where the problem is. Pull head. Punch out the swirl chamber splice block on probable cylinder and redo magnaflux to see if casting flaw in there. OR rig up a pressure test with compressed air and try to determine a leak.
Im fearing there must be a internal crack at this point.
Cat had a real problem early on with precombustion (swirl) chambers sealing. Don't rule out resealing if no cracks found. There doesn't seem to be a replacement head for sale in China or N America.
Ill let you know how it goes...