Four track build

If you have no idea already on how to make them I would advise you to not attempt to do it.

You need a welder, tube bender, bench drill and knowledge in fab work.

You don't modify the front shaft/s, you replace with new, Cobra I believe are a good brand.

As for the rear end, youl need a swing arm stretch and a shaft stretch. To extend the shaft you simply cut it in half and bore a piece of solid to the shaft diameter and press together to the desired length.
So, for the rear, you need a Lathe and a shop press.

Hope that helps.

A lathe to extend the shaft fish... Bore a piece of solid bar to the diameter of the shaft and then press the ends of the shafts into the new sleeve. A tight fit eliminates any distortion when welding and also reduces chances of it being misaligned

Could bodge it with a close fitting piece of tube I guess but I certainly wouldn't lol