Re: Frame material questions
new here, but not to cycling in general. If you get CroMo tubing, do yourself a favour and do not buy butted tubing, as it is thinner in the middle than the ends. Single gauge CroMo is just easier to deal (as in weld) with. Low temperature fillet brazing does not weaken the materials as much as MIG or TIG. Maybe tack the pieces together and then braze?
Hi-Ten steel is only about 15% heavier than Cro-Mo for a given strength, so if very expensive, just get what you can get, or hack up a salvage frame to get tubing and modify the frame you want to.