I found an easy way to get a good seal on these overlap joints.
Cut 4 slots by hand with a hack saw, from the end of the over lapping pipe straight down the pipe to about 1/4" past where the inside pipe ends. Then install the inside pipe, clamp it. Then weld up the last 3/2"-1/2" of the slot (the end closest to the end of the inside pipe). Don't weld the two pipes together. This allows the clamp to close the outer pipe around the inner more tightly, and as the welds cool, it also camps the pipe on its own.
No leaks, and it is disassemble-able. BTW, Harley camps are great for this (<8$ each from the HD dealer).
So many interests, so little time...
'76 GL1000: "The Super Bee" - finished.
'75 GL1000: Basket Case, Next project in queue