Re:
If it's a Shimano hub and a Mavic rim from that period laced with a 3 cross pattern then very likely it'll be 264mm on the front wheel and rear non drive side and 262mm on the drive side.
Mavic 231 or a Bontrager BCX rim will make it about 266 or 268mm. Many variables depending on the hub and rim combination along with lacing pattern though.
As already stated, best thing is to measure what you have, from the end of the thread to the centre of the spoke elbow/bend.
Bear in mind that it's better to have spokes that are 1mm too long than 1mm too short, as the spoke thread needs to go all the way into the nipple. Short spokes usually cause broken nipples.
Very painful.