Recently got a new used bed for my 88 w150 but can't mount it. The holes line up but there are no nuts in bed for my bolts to go into. I don't have the old bed to compare to. These holes are the back 4 mounting points. Are there clips to get? Also the front 2 mounting points have a different thread size or bolt size. I'm using my original bolts from my old bed but they will not go in. Did these bolts vary from year to year?