Not heard from Derail in a while. I did send him an email a few months back, but no reply. I hope he's ok and still racing those KLX's.
I guess that part number is a Wiseco piston.
I have no love of that make, but I do use the MTC version. These are from the early KZ1000. Make sure you use the 17mm pin version. A 72mm bore is ok with a standard liner. Mine has run for a few years like this without any problems. You will get 262cc.That was until the big end went after 8000 miles from new.
Be careful of the 12:1 compression though. My MTC piston was rated at 10.5:1 in the KZ1000. It is a bit more in the KLX !!. The valves clear the piston with the standard cam. The same goes with the megacycle cam, but only just.
One of the reasons I don't like the Wiseco is that it comes with wire clips to retain the pin. The MTC comes with Teflon buttons. Sooo much better. If you have ever seen what an errant clip can do to a motor if it breaks loose..... !
If I get a chance I will find the ebay ad for MTC in Florida and post it up. Delivery from Joe Hooper (the dealer) is excellent. Price is good too. MTC pistons are also silicon free. Yes, it means warming it up properly before thrashing it, but well worth it.