[N2TRUX]

With the template made I was able to mark my cut lines by taping the pattern in position. Once the pattern was squared and secured I marked the frame.
I drill holes at the intersecting points to eliminate potential fatigue points. A 4" grinder with a cutting disc was used to make the cuts quickly.
I purposely made my opening tight so I could grind to fit. It may not be necessary, but I plan to add tack welds at the point of contact inside the frame. With the thickness of material used, I'll speculate the notch is stronger than the frame, but adding some additional insurance can't hurt.

Sorry, I failed to take pics of the drivers side cuts. Ill add some when I do the passenger side.