Ideas on fixing this frame

[C.I.Blazer]

Got my engine pulled over the weekend and found that the frame had been cut on both sides. The engine turned out to be a 400 but my understanding is that they are the same size as a 350 so I am not sure why this was done. I guess who knows what this thing had in it along the way.

Any ideas on what I should do now? Are these notches significantly weakening the frame? As you can see, the passenger side cut means that there are no top bolts attaching the engine cross member support. Only the two bolts on the bottom of the frame rail.

The more I tear into this thing the more I want to keep tearing into this thing but I am just not in the position to do that. Should I try and patch something in?

Thanks for the advice