Motorgeek, we have 2" of solid aluminum inserted into each opening of the cut stock tubes which will get anchor welded on three sides on each end both tubes. Then going to overlap it all with plating for added strength. It will be welded in a jig by a guy that's been welding aluminum for 35 years and been instructing a welding class for 20 years so I know the welds will be done right and hold. My buddy that had the pieces machined for me is an engineer and every simulation he's ran says it will hold up to a ton of abuse. If it does break I can always have it rewelded plus I still have my stock polished swingarm that will be shelved if need be.

The 2" of solid aluminum fitting tightly into the existing side rails, appeals to common sense and helps in getting the approximate alignment, but actually adds very little to the strength in the weld zones.  The plates added to the bottom of the side rails is the component that adds strength for stresses created when hitting bumps and jumping when the rear wheels have equal loads.  Plates added to the sides and top add strength for the stresses created when the swing arm is twisted when one wheel takes more load than the other.   

  What thickness of plate, alloy of the plate and welding rod alloy are you going to use?