If your going to run a FM2 kit, go with what is proven. 9:1 ratio for compression and nothing over 84.5 mm piston size.

As BlitzWing said, since it the FWD application BP motor, you will want to keep the original coolant setup, which for us is the exit at the back of the block. This will help keep it cool under boost. The Miata's BP block had the coolant exiting the front of the motor for convince and it not the best when it comes to cooling. The rear of the bock tends to overheat so look into a coolant reroute for the Miata. There are ways around the expensive known reroutes too. I have to look but somewhere online, you can use a Kia housing on the Miata for the reroute. Or if you want to be fancy about it, you can use one of the Miata venders kits like 949 Racing or Flyin Miata.

http://949racing.com/miata-coolant-reroute-system.aspx