The NSR is not an AAC. The X-12 is a nova NS12S3 with a mugen stamp on it. If you don't believe me, then buy both of them (the x-12 is a non MCP) and compare the part numbers in the owners manual. I own both engines. They are the same..... X-12 is an NS12S3 with a taller head that is anodized grey. The only other difference is the x-12 has a standard head button, and the nova's have a turbo button. The NSR is the MCP version of these engines.

Same con-rod, same piston/sleeve.
BTW: They both rip...