Cut n stut driveshafts?

I'm guessing that you are planning to use the tube as a sleeve over the existing drive shafts? What ever you do your are going to need a good welder who knows what they are doing as the welds will be under a lot of stress so you are looking for someone who can get good penetration maybe even get the shafts x-ray tested (not cheap but better than having a flailing drive shaft at 70mph on the motorway)

I wouldn't risk it with the torque from a 2.9 turbo. I'd suspect there would be a good chance of the driveshaft breaking next to where the sleeve is welded to the shafts due to the shaft being weakened by the weld. I'd get some custom driveshafts made to the length and spline that you specify.

Cheers for your points. It will be a 4x4 so the torque will be split to an extent. I am going to drill a four holes through the sleve and the driveshaft and put rods to increase the strenght. I finished the rear today, I am using an arc welder so penetration should not really be an issue.

I think I will make another set soon, this time using a splined sleve and putting the splines onto the other end of the driveshafts. This should stop the shaft from breaking.

I can't see that doing anything to increase the overall strength of the driveshaft. The weak point is still going to be on the original shaft next to where you are welding it to the sleve. I'd also check with someone that knows about SVA tests to see if they will pass driveshafts made up this way if you're plnning on registering it for road use.