Roughly speaking, a Ford 9 takes about 2.5 quarts of oil, however it depends on the housing type/shape as well as pinion rotation. I don't know of an easy method to check fluid height without a fill plug, though I added a fill neck on the top of my housing and an 1/8" NPT drain plug at the bottom seam when I welded on a back brace for easier service. Do you have any pictures of what you're working with?