Well the case inducted motors have a large area that would need to be filled, you effectively added lots of crank case volume by going to the piston port kit. Just blocking the reed intake off and not filling that dead space limits the motor. Maybe you filled that space but you're still limiting what the motor can do by blocking that off. I'm pretty sure the crank is different too.
I'm pretty sure I have a 4 pedal setup in my garage somewhere. It will be hidden under the rizatto intake, which at the moment hasnt been mounted but it looks like it will work quite well with the 19mm dell on my pacer.