Don't worry about tracking down the grooved pistons...it's no big deal. Somender Singh's modifications were limited to work on the heads only. He is a "port by theory, feel, and testing" kind of guy and until the not to distant past had no access to formal flow bench testing equiptment, etc. He simply started out by testing an engine in a car, pulling the heads, doing his modifications keeping everything else the same, and reinstalling the heads and comparing the performance. A while back we were e-mailing back and forth with rather long winded question/answer periods. He is a very likable guy by the way. This was before he got decent access to some serious testing equiptment and started his website.
I have heard a good number of report from serious racers(mostly drag racers) who have done strait A-B test taking their heads off, cutting the grooves, putting the heads back on with everything else being exactly the same. They have almost universally been reporting noticably improved idling and low end torque numbers with longer duration cams. The exhaust temp is said to run cooler with much less carbon build-up from combustion chamber through exhaust pipes. All have reported significantly improved detonation resistance. I have heard plenty of people who have tried it and say good to great things, but I have yet to hear of anyone who has tried it and was disappointed. I am naturally very skeptical of the just sounds too logical and simple to be true, but the functional feedback I've found seems to be about 100%. Interesting!