Yeah they under rated a lot of engine specs in that era to keep the insurance companies out of consumers pockets. However, I've read many articles that have found the stock 340 (`68-'71) to produce right around 275-290 hp. In this case it sounds like Chrysler was not trying to dupe the insurance companies. You have to read those hp ratings carefully though because (for example) they will rate a 426 HEMI at 425 hp but measure it at a lower than average rpm to keep that hp rating low and avoid outrageous insurance premiums.