im not sure about the CA smog. I don't see how these would affect anything exhaust related but Im not an expert on the laws there. You will have to check on local laws and install at your own risk. Man-a-Fre and SOR sell OEM tanks when they have them and non OEM tanks also.
When installed the subtank is only noticeable to some one that knows these trucks well. This is not to suggest trying to skirt any rules. The diligence is on anyone installing these into their trucks. I've been running one in AZ for a few years and never had any trouble with emissions or local laws here.
Cool. I'm honestly not concerned. Put me down as maybe on an 80 and ill confirm with final price.