I am restoring an old Harley motorcycle frame and need to replace the backbone with 4130 tubing. when the frame is assembled the stress on the backbone joints is a "compresion" stress on the backbone. The backbone slips into a cast iron form at the headstock and at the seat area. Harley, during construction of these frames would "sweat" the joints with a brass or bronze filler. The joints are 1.5" diameter and about 1.5" deep. My concerns are obviously the safety aspect of racing a motorcycle frame with this type of repair and the correct process in the repair procedure to address this safety concern, but also the risk of ruining the cast iron sleeve on the cast parts by applying too much heat while trying this brazing technique. My thought is to actually solder the joints with Rockmount Gemini-S solder & Gemini Solder Flux in an attempt to maintain a lower tempature with an oxy/acetelyne torch with the rosebud tip, thinking that the joints on this repair aren't as critical as other types of stresses on a soldered joint. Would are your thoughts and suggestions?  Thanks!!