Mechanic cut frame to fit headers, how bad is it?

[Brody54]

Hey all, it’s been awhile and my truck has been getting worked on over a year for an engine/ tranny swap. The engine came from a 69 Camaro but same thing, small block Chevy and turbo 400 out and in. Just higher performance and a 383.

Anyways the mechanic kept the headers from the Camaro and cut the frame to make them fit. I’m not happy at all and looking to get a second opinion. How bad is it, and my concern is the frame cracking eventually.