If you want to do your own legwork and decipher your own, the RPO codes can be found in the parts manual you can download here:
http://67-72chevytrucks.com/vboard/showpost.php?p=5621043&postcount=1
Note that GM recycled and/or used the same RPO for cars and trucks throughout the years, so some RPOs (like G80) mean different components in a car or truck, vintage, GVW, etc.
The "universal" RPO decoders arent terrible, but most seem based on a car RPO list, so there could be some RPOs that are different on a truck.