will a cckb onan fit in a 6018

Center line of crankshaft height is different between B & C series engines. Doesn`t mean you can`t make it work. But IIRC it`s not a drop in

I think that room for the CCKB would not be a problem but that's something that you could determine quickly just with a measuring tape.

As I see it, here are the issues you would face.

- having to create a custom exhaust system.

- some rewiring because the CCKB has an ignition coil that is controlled by the key switch whereas the existing engine may have an ignition switch that KILLS the spark. The charging system would have to looked at and the wiring would have to be modified accordingly.

- the center-line of the crankshaft to bottom of the pan is a distance that you need to take note of because the lines to the pump don't have much leeway.

- choke and throttle cables may be too short or too long as well as the fuel line.

- lastly is the pump to engine issue. I doubt that the existing pump mount would work but it might. The issue would be the bolt pattern on the block. The size and length of the crank stub is also an issue. The stub on the CCKB can be cut down to the right length and a different coupler can be used if the diameter is different. However, it must be a straight output shaft with a keyway, not a splined shaft or tapered shaft.

In other words, there are no major issues. Just some small ones that can be addressed fairly easily. Since you have to yank out the existing engine anyway, all of the issues can be examined once you have both engines sitting side by side on the bench.