Veronica, if you aren't totally paranoid about year correct originality you could put what the 66's got on. My 66 and all the others have a rubber pad that clips onto the inner fender so the positive terminal doesn't touch.
And I am confused about 2 things, what do you mean your battery is in backwards? I thought the Mustangs were supposed to have the terminals towards the back. Also, on the battery cover, is the positive mark on the side that goes by the inner fender, or is it on the side closer to the engine?
1966 Mustang Sprint 200 "Oliver"... factory fog lamps, factory rally pac, off the road for restoration.
2005 Mustang 4.0 litre... Airaid CAI, Honeycomb taillamp panel, more mods to follow.