Mikey, Here's what I'd do out in the back yard.
Get a few of the these and cut the first 8- 10 inches out of each tube..one at a time.
Slip a piece of these of the appropriate size into what you've got there.
You don't have to be a welding pro because the smaller tube is going the right way, if you follow me.
You might be able to slip the tube into the 1 and 5/8 stub on the flange. Mig weld or braze it on the outside of the flange. De -burr and roll the inside edge ,and you got it.
Doubt if it will hurt anything..Might tell you a thing or two.
http://www.speedwaymotors.com/Mild-S...Inch,1734.html