Jerry, tangs are never the right shape or curvature as received. Hawken tangs may be the worst. I have no idea what original rifle they were taken from, but IMMHO, such a rifle doesn't exist!
To start with, al the tangs I have worked with have been made of malleable steel...can be bent cold. But, many tangs require being bent right at the breech plug journal, or very close to it. To do this, I use red heat from a oxy/acetylene torch, heating only the are the needs to be bent, and then a heavy hammer to apply the bending force. One or two good hits is better than a bunch of taps. I do not want to rivet the steel out - just bend it down. The same ca apply to the rest of the tang, to get it to follow the pattern you have. You have a pattern, right?
Once that initial bend is in, a long tang may require bending in small increments along its length. Here, I use Ken Guy's method - three vertical bars clamped strategically along the tang, and gentle pressure on the vise handle. Some tangs, such as cast Hawken tangs, also require lateral bending, and these bars do the trick again in this case.
Occasionally, I just put the end of the tang in the vise, and using the barrel for the handle, bend away. This is only when the bend is small and along a uniform thickness of steel.
