is the GVW the best way to tell a big block?

[vettedad61]

I have a 1972 Super Cheyenne big block, I was told it's a factory big block truck, it's a non-original engine (1973 454) the build sheet is long gone and the spid is missing, its been repainted a different color, the VIn in the cab is original and matches the frame, factory short bed, low hump, no heat sheild but has dual exhaust hanger.
I am trying to determine if this is a factory big block truck based on the gross vehicle weight on the VIN plate?

http://67-72chevytrucks.com/vboard/s...ight=vin+plate