[RDMumfts Stang]

That would be the easier way, unless it has been painted over or removed. Mine has long been illegible.

The gear change will be significant. I haven't had mine to the track since switching from 2.73s to 3.73s, but it can be felt seat of the pants. If you have 2.73s and jump to 4.10s, it will be like removing your overdrive gear on the highway.

As far as putting them in yourself, if you have the right equiptment and know what you are doing, you could install them yourself. I would venture a guess that most people take theirs to a specialist. I had to upgrade my 7.5 diff so I just bought a Ford Motorsport 8.8 with 3.73s. That was before the price on them jumped considerably several years ago.