The OP wanted to attach a disc brake mount on an existing frame with track drops. The position of the caliper would cause the wheel to scoot when the brake was applied. The whole drop could be replaced with a low mount but it's 7005 and machining a whole new drop would be very costly. I told him I can't help him but gave him some info on a guy who builds aluminum bikes in the Boston area.

The aluminum frame you are looking at weighs five pounds and with a 6" travel fork is nearly unbreakable. I can't explain what the gussets do. They often appear on bikes I make. I know they need them because I know the frame would fail without them though I have not built any without the gussets. I could draw a picture with colored pencils that explains it but there are lots of engineers around here so I will spare myself the embarrassment and let someone explain it who can verbalize their mechanical thoughts better.