It's difficult to see one way or another from the supplied picture and the op is away. He'll know as soon as he compares it to the others. It'll be interesting to see what the result is.
I think the gap you are talking about is normal, its the drain from the oil ring (it helps to lubricate the gudgeon pin), much like that overly large groove behind the oil ring on the thrust sides of the pistons. These are not performance pistons and I would refrain from using much more than standard boost levels or excessive RPM with them.Looking at the picture of the piston in the block it certainly looks like the casting is broken in the area between the gudgeon pin and the oil control ring. If that is the case, you'll definitely need a new piston.
I agree with you, they're not a good piston to use in his intended application.
No need to confirm it, there is a gap in the lower oil ring land right above the pins its supposed to be there..........
For example, picture of the superior 21253 piston
And here is the 21250's sister the 21251
Edited by Sprocket, 19 January 2017 - 11:43 PM.