I remember where I saw Mobile Catholic records; not at the AL Archives, but in the Family History library catalog. You can search the catalog online at www.familysearch.org and click the tab to search the library. Then search for Mobile under Place Names. There are several Catholic Churches listed, hopefully one of them is what you want, and it covers the years you need. Be sure to click the button to View the Film Notes for each listing, it'll tell you the type of records and years covered for each.