I recently adjusted the mileage up by some 40,000 on a replacement cluster for a 240. I haven't had to take my 740 cluster apart so I don't know how similar it is but I think it is pretty close.

On the 240 I took the speedo loose from the cluster - needed to replace the small gear that always breaks off a tooth or two causing the odometer to stop working. I removed the broken small gear and then used a bamboo shish-ke-bob stick - pointed like a toothpick on the end but long and stuck the pointed end into the large gear until it was tight. then I put the other end of the stick into a hand drill and started it up - it worked great and I was able to add over 40K miles in about a half hour. I would only run the drill for about 5 minutes then let it cool off. Once I had the correct mileage displayed I removed the stick, inserted the new small gear and screwed the cluster back together.

Don't know for sure if this will work on the 740 but good luck!