The big GMC V-6's turn slow and guzzle fuel. And from all reports I've heard do not respond well to modification.
I can see it in a restoration, but its hard to imagine putting one in anything else.
That said the GMT400 series trucks accepted a lot of different motors including 454's. How does the 478 compare dimensionally with a 454?
I've never seen published dimensions on the bigger V-6's so have no idea how big they really are.
