If you ae replacing the speedo, you can reset the mileage to read what your original unit says. It's not too hard to do. Yes, to do so is against federal law, and I'm not suggesting that you lower the mileage of the vehicle, as that is the "intent" of the law, but to make the new unit read correctly should not raise any flags while licensing, transfering titles etc.
When I did my swap, I went to the V-6 guage cluster, to have the tach read correctly. I reset the speedo to 00000.0, and that is legal, as I have the original to back up the actual mileage.
Make sure you get a V-6 speedo, they are different then the 4-cylinder units.
Kary