I just checked the cowl on my 1/26/71 SPD GTX,has the snap in screens the screw holes are present but I can clearly tell there was never any screws driven through them,the screens are burred in the burred trunk,I know I have parted several 71 Bs & can remember removing screws I actually thought mine where screwed on its only been apart since the early 80s,I most likely have both types around somewhere including the screws.