Those subjects are fine, you need Maths Physics and one other A-level in-order to do mech eng. You don't even need to have done Mech modules to get in. It is applied maths they look for, but i suspect stats people should not have a problem either. As you are interested in Oxford you need to make sure you are getting A in all those subjects and that you have a really good P.S, and are ready to do a tough interview, in competition with many others applying for the same place.