I imported a '94. Emissions was no problem (will need to keep a copy of EPA statement) and I had to convert seatbelts from on-the-floor Canadian type (would be similar to air bag car belts) to the roll-up-in-the-door type (and get DOT statement that it now conformed.)
I did not *have* to convert the speedo (the oil pressure and water temp are also metric units) since both mph and kph are there, just that mph is in the smaller numbers. The importer taped a note to the dash reminding me to look at the "other" numbers for the US.
I changed speedos later, it's very, very simple. Remove dash, two screws that hold the gauge in, and unplug the wire. Reverse order to install. Why change the odometer? I took a picture of the old and new side by side for my records, and I've been told the ECU stores real odometer values anyway. The only gotcha is if you go to the dealer for service and they want an odometer value to see if it's still under warranty... but then we're back to the ECU.
Just make sure you have the EPA and DOT statements; while I haven't sold mine, it seems like the type of paperwork that any future buyer might need to get the car registered in their name. Since the VIN will flag the car as non-US, somewhere down the line you'll need proof of a legal importation.