To come back to your original question. Yes you can't really be 100% sure. Unless some apron work is visible and against the claim of the seller. In my experience, I know I find very strange that 35 years ago, there were already at the time a few 429 CJ's registered and now days, since value went up, it's like Ford had a secret production of SCJ's. So yeah do not buy without inspecting very very closely.
Some parts absolutely impossible to find may also help. For instance a CJ with a rochester will have a mechanical pump with a return line. This metal line goes back to the tank from the driver side and is hooked to the tank sending unit with 2 in-outlets. The holley equipped do not.
if you can (and should) look at the car on a lift. Try see which kind of converter is on, as the pilot is larger for these than other years (may be the converter part number could help id/comfirmed that). The tag on the c6 as well. They have extra planetaries vs regular C6 coming for instance from T-birds(tho some had these).
The heads must have the stamp DOOE-R...
The more original parts 71 only , 429 only you find the less likely it's a scam as finding these parts is very hard these days and requires a significant investment in both time and money. History of the car can help as well etc..
Good luck finding one and keep in mind there are also honest people!
