The backspacing will be close, but I think the pre-03 wheels will stick out slightly. IIRC the Vic wheels have a 15mm offset. I think stock Mustang wheels are 24?mm. I bought 0mm offset wheels for my Vic. I knew the 24mm wheels wouldn't work.
Also make sure that they are 16" 98-02 wheels. Pre 98 wheels were 15" and you'll have to ensure they will clear your brake calipers. 03 wheels have 54mm offset.