It is easy to take the onland wheel off. Turn out the bolt on the hub, pull out a pin and the whole wheel and hub should slide off the axle. Clean out all the old rock-hard grease and oil the spring that holds the trip lever. Might be the axle pin is missing to make it move in and out so much. You will easily find the problem as they are simple things to work on.
Your moldboard looks good to me, if you can plow in some sandy soil (not rocky!) that rig should shine right up. A John Deere R should be a good matchup for that plow!!!
LA in WI