Hello,

The SHIMO3 comes indeed with some extra shims to play with the manifold length, but since I have not received them I cannot tell you more in detail for how its made and applied. So we have to wait a little untill I have them in my hands.

As for the OS manifolds, yes indeed I agree that there is no real clear measure and of what they should really gain
MR02 is the one which is bend down and gives you the usual look with the pipe horizontal.
MR03 is the horizontal manifold quite long and make the pipe touch and melt the body very often in that area. This pipes gives you a better low-mid RPM but less top rpm
MR04 is also horizontal and shorter then the MR03 shold give better mid and top rpm
MR05 is for me almost the same, cannot see a lot of difference but according to to OS works the bes with their 2196 pipe.

In the beginning we used a lot the MR02/2165 combination.
Now the best combination is for me the MR05/2196 combo but also uses a little more fuel.

Many combinations are possible but I suggest you try and keep things as simple as possible to get a relaiable engine and power.