I did this with my Duster (my first ever attempt at body work).
A few things I learned.
I really didn't need to replace the entire quarter panel. I really think I would have been better off cutting more manageable patch panels.
Be prepared for more rot underneath
A good spot weld cutter is...
I just broke the rear window in my 74 duster. Seems the window seal didnt want to let er go. But any way i am just curious if any body has had to replace this window and how much did it cost.
Well it seemed to work i got rid of the hole and the rust, and it looks good. i dont have the car on the road yet so only time will tell about my patch job.
If you want to play it safe call the frame shop and see if they want the engine in or not and let them fix it. i had a similar problem with a hole in the frame on my 74 duster. i just cut the bad out and patched it up with new metal