You can never really know what is in a used truck regardless of what the previous owner says and it only gets more challenging as the vehicles get older.
I always am honest with what I know and what I don't but I am sure that some people that have purchased vehicles from me find something that I did not disclose. Unless you have an intimate knowledge of every parts on a used vehicle there is no way you can know/disclose everything.
In your case 12v conversions can be sketchy depending on who did the work and how much depth they went into. My 1950 was claimed to be converted but I didn't care as the electrical was all being stripped out and replaced anyway. Engines that are not original are pretty common on trucks of this vintage as back in the day engines didn't last as long as they do now and it was cleaper to swap something from the junk yard than rebuild even with parts and labor costs what they were back then.
