Here is the "poop" on the RIK/Mitaka pistons. I just got a set in from Reproductiondecals, first over 400.
They came with Riken rings.
The wrist pin is 14 mm instead of the stock 15, but comes with a bearing to make up the difference.
The clips are a strange "G" type.
I haven't checked the rings in the grooves yet.
No directional arrow
The piston edge is approximately 1mm lower than stock.
This takes the compression from 6.5:1 to 6.32:1
Compression goes from stock 143 to 139psi
This adds about 4.4 degrees to the exhaust timing
It adds about 5.5 degrees to the transfer timing