If my measurements are correct, though it may require crushing/cutting/forming the Factory oval to fit inside the Rectangle tube, as the Oval is JUST under 2.5"x1.5" by like .240" or so, so the 16/14ga should work, maybe even 11ga or .120 should do, but won't know until I can try to source the rectangular tube locally (Not fond of spending almost $30 for steel just to take an irreversible chance). Far as the down tube and top tube are concerned, was thinking of getting the 1.75+ tube, find a size that fits snug into that, cut the 1.75 to length, drill about 4-6 holes into each end in an X pattern around the ends,cut off about 4-6 inches of the smaller tube, slot it halfway into both ends of the 1.75 tube, weld them together at the holes. That way the fill-in tube has extra support at the joints, then finish welding together. Kinda hard to explain (never was good with explanations, was always the hands on type), so once I( get my project underway, I'll upload pictures on ym progress as well as any road bumps I might run into.
Looked at them, seen for 2' is about $24 shipped and round tube 2' for $about $35 shipped, but if I can get a hold of a place near me for cheaper, rather go that route. I have people to do the cutting/welding for free, just need the materials.