Probably based on the R2106 which its crankshaft has a much larger timing than all previous models.

The shims are no sleeve shims but exhaust shims to lengthen up the exhaust a tiny bit for a little bit more bottom torque w/o the need for a different manifold. Funny thing is that a year ago I placed this on my FB page, just quick and dirty made for a test and nu I saw this Shimo model. Makes you wonder where he got his idea from....