I am building a new motor for my 66 and have a 90 block. There are a number of differences in the castings. I am wondering if anyone knows the purpose of what seems to be a vent hole in the left side of the bottom of the block into the crankcase. There is a little notch for it in the oil pan gasket. It's not in the 66 block. Does something go in there to keep water/dirt out. Does it need to be plugged? Thanks for your help.