I remember back when I was in my early 20s, I put Big Blocks in 2 different small block cars without have to modify anything. 1 Dart & 1 Challenger. I don't remember what I actually did to make them fit but I didn't take moving and modify the k frame. Just wondering.
I have a 340 Dart GTS convertible and I had to cut out part of the drivers side k-frame mount so the big block oil pump would fit on the k-frame, I still have that car with the cut...