To my knowledge this is an XL185 motor, with bigger piston, valves etc and this is what you are trying to say right ? and There is no CB250 engine that is similar to same 100-125 design. All those are twins, CB single Cylinder motors are CB100, Cb125s, CB125Jx (Same motor), and CB250RS (Most powerful) and a CBX 125, with DHOC variants in different markets.
baki CB250n hai jo twin Cyclinder hota hai..
This is for all those who say Cb250 motor, To my knowledge this thing For sure is an Xl185 motor, and could be bored up by you guys. as you said so