It's more likely that what you are hearing is loose motor mounts or a drive clutch that's getting sloppy. Both should be due for service @ 1300 for sure.
But to your question about the pistons, there is no real way to know without pulling the cylinders and inspecting everything... but most of us believe it's a good idea to replace the pistons by 1500 to 2000 miles. Chances are you will find ring flaking and knife edging of the piston skirts. If you drop a skirt, things get expensive fast.
I always recommend the MTNTK fix kit for a few reasons:
This kit has been proven over many years, is reasonably priced, and MTNTK is great to deal with for support / warranty. I find most other vendors don't seem to care unless you have a $10,000+ build in their shop.
