I would be surprised if it was heat treated so hard that you can't machine it. That would make it too brittle.
Now the parts inside may be hardened. It is easy to find out. Take it to a heat treater and have them Rockwell test the surface hardness. They probably won't even charge you.
Bob Shaw

87 Raizer, 4.3V6, Mod TH700R4,231CHD, detroit rear and LSD front, bouncy seats, 2" lift and 32x15 BFG MT tires.