I have looked through the previous threads and can't see an answer to this, so perhaps someone can put me right.   As I understand the wiper racks are the same on pretty much all models, but it looks like when fitting a TR6 motor to an earlier car changing the wheelboxes is also suggested. Is this essential? Is there anything to stop me fitting a TR6 motor to a TR4 rack/wheelbox set up? Does it affect the sweep angle significantly or is there some other subtlety that I have missed that means