Another angle on a swap is that the early Stihl 018 had a 8mm wrist pin whereas the later 018 & MS180 has the 10mm wrist pin.
Therefore you could get a 38mm 180 cylinder and buy a Meteor piston for a 018 and use your old crank but that would cost more than buying a used crank. You can get a Chinese 38mm piston and rings with a 8mm pin for $18 + $2.75 Shipping on Ebay and that way the price would be about the same.