Originally Posted by
FBinNY
If you have access to a head tube mill, you can quickly mill it down to below the cut and have a nice cheap frame.
Ding ding. That's the correct answer.
A shop may even do it for less than $40 because it is just aluminum.
I'm assuming that the notch got there because someone wasn't paying attention with a saw or had to cut out a frozen headset - not some sort of crack or defect.