57taskforce and turp_mcspray got it right. This picture shows what you are talking about - looks like this frame cut was forward enough to require moving the cab mount. Wow - can't believe no one who looked at this yet caught this. I guess that cuts the value way way down. At least it is still a big block 396!
https://www.dropbox.com/s/6o1mi3j30bluiwf/010.jpg?dl=0