Hello Detmatt,
you are right. The HP stamp is for the 335hp 68-70. Thru 67' Chrysler basically made 2 383 engines, a two barrel, and a four barrel engine. If it is a four barrel, the 67' is a 10.0:1 engine and 325HP. in 68, there were three. 2 barrel, 4 barrel, and 335 HP. Bill Brownlie wanted something to make the new Roadrunners/Bees different, for advertising purposes. The HP engine came with heavier valve springs, higher lift 440 magnum cam, a windage tray, and double roller chain, and a 440 HP transmission if an Automatic (8pinions). They were advertised this way. All for only 5 horses. These were roadrunner and bee engines only. Charger and sport Satellite, and all other 68-70' mopars with a 383 four barrel had the 330 HP engine, (7) pinion transmission. What is interesting, is Chrysler used the H engine designation in both the charger/Satellite, and roadrunner/Bee, and any four barrel 383 car. (this Info can be found by googling Pau A. Herd, and Mike Mueller authentic restoration guide, charger,roadrunner&superbee.Printed in 1994) Also Bill Brownlie, creator of the RoadRunner and Superbee. I presently have a 69' 383 cuda,and 383 GTS numbers matching, and no HP stamp,as well as a 68' Sport satellite drivetrain, four barrel engine and trans vin# matching to title, ,no stamp. So don't worry about it. If it has an original 67' four barrel, and an H in the vin, your good.