The latest issue of Warbirds International: Mustangs has an article on tests with ski-equipped fighters with, of course, emphasis on the testing with a pair of P-51A's. The P-51 seems to have fared the best overall, not being particularly deficient in any of the test categories (other fighters - the also tested the P-36, P-38, P-39, P-40, and P-47 - may have excelled in one area, but the Mustang wasn't behind by much, if at all, in any category). In any case, the tested retractable ski landing gear was never adopted, but I could see ski-equipped Mustangs in Swedish or Finnish winter camouflage (the Finnish ones perhaps being captures Soviet examples?). The article does have enough pictures that an accurate model of the installation could be made.