Non matched pistons found in engine

I have a 1974 XKE V12, American spec I assume (was purchased in USA).

I got it with known engine issues. I am the second owner of the car, I do not believe any substantial worked had been done on the engine. The story is that is was running poorly and was DRIVEN to the mechanic, they never fixed it, it sat.

I pulled the pan and found things looking pretty good, except for piston "6B" which is cracked and some cracking on that same cyliner.

Looking at the nuts on the inside they all have untouched little blue paint marking and look factory to me. Does not look like anyone was in here mucking about.

BUT...

Not all of the pistons are the same. 4 of them look a bit different.

Here are pictures of the two different types of pistons I see. Four of the pistons have a flatter area below the wrist pin. They are from completely different castings.

http://www.clery.net/jaguar/FlatBottomPiston.JPG

http://www.clery.net/jaguar/RoundBottonPitson.JPG

Could it be the factory built the engine with unmatched pistons? Do they just grab whatever pistons are laying about ?

Or, do you figure soneone was in here and replace all but 4 of the pistons ? Also odd.

Thanks for any input,
Bill