It's fairly simple to reset the odometer and quite legal in the UK unless you're doing it to deceive a potential buyer of the vehicle.
You just dismantle and use a small screwdriver/penknife to release the pressure on the aluminium levers that hold the individual odometer wheels steady, then you can select whatever numbers you want. If you try to just push the numbered wheels backwards from the front then they will move but you'll bend the Al strips and get that tell-tale misalignment when back in service, plus of course you might mark the white lettering.
Reset ? It's a personal thing. I did with my Europa but not with the Elan following body-off rebuilds. In your case Joe I think I'd try to get a new speedo to match the rev counter and leave the original one alone. (although only an enthusiast would know they're not a matching pair, it's a good choice you've got there)
Brian
