[mickmate]

Steve, I would use a 1020 DOM seamless tube with an ID a little smaller than the axle OD. Put the axle between centres on a lathe ( centre holes are already there ) and turn down to your next standard tube ID. Calculating the CSA ( cross sectional area )of the shaft backfigure to the required OD for equivalent CSA of tube. This will be more than adequate as you have the advantage of the increase in circumference for torque transmission. I would plug weld tube to the shaft as well as welding round the ends. ERA has some good info on their site also. Interesting you're widening not narrowing, do you have an E type rear? I'd be interested in talking to you more if you need help as I have some Jag axles and a lathe just waiting to meet each other! Good luck.