Name tag engineering do work on two stroke engines, their work on the Leader/Arrow engines is said to be good. They may be able to machine the journals/shafts to fit the smaller bearings but I think the only way be get the required accuracy is to split the assembly and machine the shafts separately.
To get the bearing to slide onto the shaft but still hold firmly enough not to slip/spin requires a tight tolerance in the order of .0001/2 '' . I finished mine off with a slip stone to take the last .0001/2 off and get a tight fit on the inner race of the bearing. It's been OK for 20 years and nearly 18,000 miles.