Went to RockAuto.com the other day to get some freeze plugs for our '57 y-block. The ones they had listed were 50 something mm and when I measured the holes in my block they looked to 40 something mm (or vice versa, either way it didnt seem to jive) Did I measure wrong or are there different sizes available for different blocks???I am really going to push to have this thing fired up for you guys soon!!! thanks-