Has anyone had good or bad experiences with aftermarket pistons and rings on the larger isuzu 4 cylinders?

I rebuilt my 4BD1T two years ago using after market pistons, rings and liners. The liners (chromard) appear identical to factory items.

I spoke to a diesel mechanic this week who works on 4BD1t and 6BD1t bus engines, all the aftermarket pistons he has seen in use have cracked around the 100,000km mark.

Given the large amount of blowby my engine has had since rebuild (almost the same as before), I suspect the gap in the aftermarket rings (which I didn't check) is also too large. I have heard 3 thousandths gap for every inch of piston diameter, is this a good rule of thumb? Anyone know what stock new items measure at?