What appears to be rust could actually be congealed and burned synthetic oil or even castor oil. If it rubs off easily with a finger or a q tip then you are probably OK to run the engine as is. If it is rust then you will need to heat the engine to about 250 dgrees F to get the liner out which will then make it possible for you to get the con rod off the crank pin. After the crank is out (heat might be needed here as well) heat the case again an tap out the bearings on to a wood block. Sometimes it takes repeated attempts or even a little more heat to get the job done.