Firstly make sure your engine has enough grunt to chip at a production speed maybe up to 60 hp, I allways believe it's better have more than you need then if you need extra it's waiting, Then I would re inforce the impact bed under the anvil.this where they seem to fracture and it's a hassle to fix up in position, I know because I cut our's out and fitted a thicker section, Definately a strong lift and crush,scrap three knives and keep it balanced have four since now we power to run them,hydraulic drive to the wheels would blow the project out of the water but if you have the money make it an option, The pull out tarp a good idea but seriouly how long would last, Fit a winch to it and you can use this to pull it around a yard for position and anything else that comes to mind and provision for a brake device/tag line
so you can manipulate your sections coming down, How many times have you had to bust a gut pulling the sectioned just lowered away from a target below?, Kill switches at all four corners of the machine and more storage room. This is all I can think of at the moment.
