I need some help. I replaced a carb that was not made for the 67 engine with a correct motorcraft 2100 (manufacturer rebuilt). I went to switch the air cleaner hold-down screw to the new carb, and there were no threads in the hole. Not only that, but the walls of the hole did not get thicker on the inside, so I can't tap out or thread the hole. This is my first carb project, so I'm at a loss. Is this common and how can it be remedied? I have had no luck finding an insert to go sown in the hole, either. Thanks in advance.