Swapping engine sides for the valve covers will make the normal front of the right-hand one be at the back of the new left-hand location (and vice-versa). If the breather port is supposed to be at the front to prevent
oil ingestion during acceleration, then its new location at the back could produce the results the current owner describes. On the other hand, there are other reasons for an engine to smoke under hard acceleration, so the description is plausible, but not definitive. If the covers are swapped, this could be no big deal.
Anyhow, I notice everyone here has an attitude that if you aren't going to Jay for your BDR, then you should run from the deal. I would look at the deal under its own merits and make a decision for yourself and avoid the sheeple mentality. When everyone is steering you from a deal only you know the details of and they are steering you toward a particular source, sight unseen, that is when to run (not walk).