He told me that it was listed on the build sheet and gave me the VIN, but when I looked it up, there was nothing about LPG. Asked him (by text), he said it was the reference to "6 extra gallons of gas" - which of course just means that Chrysler credited the dealer with putting an extra 6 gallons of petrol in it.
When I pointed this out, and also said that there's no evidence Chrysler ever sold the ZJ/ZG with factory dual-fuel, he suddenly snapped back with "It's sold", so I'm now fairly sure he was bullshitting me and he's trying to sell a ZJ with a completely undocumented LPG conversion (he said he didn't have a certificate or any other documentation for the LPG because he didn't need one, it was factory-fit).
I'd prefer to think he was genuinely clueless about the build sheet and he really believed that it was a factory conversion, but the sudden "It's sold" was a massive red flag. Hey ho.
I'm not particularly after a 4.0L with LPG anyway, but the price was right to use as a station-and-back runabout.