If your 4020 has had 18.4x38 rear tires or some equivalent large diameter tires installed, the draft arms can be too short. Late model 4020 and 4320 tractors with large diameter tires were furnished with longer draft arms. I do not remember 4020 tractors with 15.5x38 or 18.4 x34 tires ever having interference problems with regular draft arms. Hope this helps.