My dad has an old 6-71 detroit diesel that he is going to junk. Obvious question is how much work(machining etc...) needs to be done to get it onto a 454, and if it can be done at all. thanks.

Lots. Don't bother. I was given a 671 by a fellow who is now sadly no longer with us, and I might some day redo that one because there is a sentimental value to the blower, but otherwise......