Originally Posted by THE DOCTOR
It is not the RB it is the Mugen X12. If there is a differance. The engine sheet that came with the engine shows the turbo button part #NOV28605 and the standard button #NOV28604. Anyway to find out if this is the same one as the MT12?? The sheet also shows a bore of 13.8mm.
It will fit in the cylinder, and properly shimed will give you same compression ratio as all other Nova heads.
Problem with MT12 head button is that it is thinner than all other Nova based head buttons, and the cooling head will hit cylinder crankcase before proper sealing torque is applied to head button.
AFM