The main backbone is oval and where it meets the steering head it is not connected to the down tubes at all. It just floats in between. So I put 3 plates in to tie it all together.
I put a tube inside the backbone and T'd it into the rear down tubes. The inside tube was built up with pieces of 1/4x1/4 stock to approximate an oval shape. You can see 3 stitch welds along the top tube. Those welds catch the pieces of 1/4 stock. These stitch welds are located on top, bottom and both sides.
I had CMR cut 1.75 inches out of the front down tubes. The connection is reinforced with a spigot inside and pinned. You can see the 2 circular welds and pins.
At the back, above the swingarm pivot, they cut thru the down tubes about 90%, applied heat and bent the frame down. To shore up that area an additional cross tube and square plates was added.
PS, you'll note a ring around the inner tube aft of main oval tube. That just ties all that together.
Thanx Brian.