The C series had a few differences, bigger tires and different seat, the engine had motor mounts, has rubber isolation type mounts that use a different oil pan. Because you'll going to use an engine that did not have the engine mounts don't use the rubber mounts and I believe you will be OK, may have to drill some new holes to directly mount emgine to frame. If you where going with a K181 from a non C series you could just swap oil pans, but because you are going to bigger engins the oil pans don't match.
Just discard the mounts and you should be ok. I have done this myself. Good chance you will have to change drive belt as well. See if you can get the pulley with the replacement engine, this will tell you if you need a different belt. Check crankshaft diameters as well, just to be sure.
Hope this helps