I have done a few cutting edges from QT400. Just did one last year for my 910 loader . We drilled it for 3/4 plow bolts then counterbored for the heads with another drill ground to suit. the square holes were done by torch using a little jig lined up over the hole to run square. It looked like the real thing and stays tight. It was a 3piece edge long center section and 2 side edges ,i beveled both sides so it can be flipped around for wear, beveled the long section with my track cutter and torch then the 2 side edges on the milling machine as an effort to keep the heat out of the bevels.
I have done them for 1" bolts by drilling then counterboring the for the heads with a fly cutter that was piloted in the bolt hole. At that time we had a square broach made up which could be pressed thru ,making the square. I still have the broach stashed away ,ill try and post pics on the weekend when i get back to the shop.
All this said if you have a decent drill press ,experiment with grinding a drill bit ,run it nice n slow with cutting oil .I dont think a roto broach has the cutting surface area to stand the pressures of drilling that stuff. Im sure theres better advice on here as to actually grinding a drill bit for this material,for me i can get it done but grinding each drill bit is a science project some work well some dont.