Modifying angle of oval chainstay ports on bottom bracket
I am going to build my first frame using a Llewellyn slant 6 double-oversize lug set, its going to be pretty big (61cm actual seat tube, around 65cm virtual). I've been drawing and redrawing to get all my angles, top tube, fork length, etc. just right. The problem I am having is that to get the bottom bracket drop where I want it (70-75mm), I would have to increase the angle of the chainstay ports on the bottom bracket by at least 2 degrees. With a 73 degree seat tube, the chainstays are 8 degrees from horizontal, I need it to be closer to 10. There isn't really another bottom bracket choice with a better angle given the tube sizes I am using (31.7 seat tube, 35 down tube.) I am not confident enough in my brazing skills yet to do fillet joints to a blank BB shell.
I've seen a couple references to people using steel bar in the ports to bend them, then hammering them back into shape. However, these chainstay ports are oval, so what would I use as a lever?
Anyone ever modified a BB shell this way? Any ideas?
I've never had to make significant modifications, even though my chainstay angle is usually a few degrees different than the shell was designed for. At most, I tighten up the lugs a bit by inserting the chainstays and shell into the jig at the proper angle and then whanging away at them with a short length of aluminum bar and a hammer.