Nothing, I have swapped from 3:31 open diff to 3:73 LSD myself. It's a magic combination. No one has a fix for the speedo and convenience display (range, mpg, all that stuff) because vehicle reads it from the ABS module instead of the ECU or some such modern car nonsense. You'll have to deal with a speedo that's off and hand calculate your mileage. Everyone is upsizing the tires on their Transit though so everyone is dealing with it.
With 245/75-16"s my speedo is off right at 7mph at freeway speed. I've gotten used to it.