My experience with Nicasil is that the pistons and rings wear out while the bores remain in good shape. I know tuners that believe the bores should be highly polished 1500 to 2000 grit as a finish -- with new rings and pistons they get leak down test that are close to 0%. I have not done that. I used a flex hone that was reccomended and it was 280 grit. I subsequently used a hone that was sent by the company that did the Nicasil coating and honing and it was much gentler, probably 500 to 600 grit. The goal is to avoid piercing the surface coating.
What I took away from this was that the rings will bed on a highly polished bore if the rings are new and the correct type for the material and the bore not glazed and in decent shape. You can use a lower grit as I did, but the swarf from the rings will be much greater (which did not bother me this time.)
I would have done a leakdown test to see where the extra cankcase pressure was coming from. Short of that, If you are runing specialoids, I assume that they are worn out, but only measuring will tell. It sounds like the ring grooves may be worn out. The racing pistons I use initially showed distress due to overheating. This was cured by moving the top ring down further away from the crown and ceramic coating. I do not think much of knurling, but it is probably fine if you are not going to run the bike much. I would not run a knurled piston. The timed breather works fine if it is timed properly, but its use has fallen out of favor. I can send you some articles on the breather if you contact me at
daviddunfey@aol.com.
Good luck,
David