No, IHRA says that for "rating" purposes relative to other combos. The Commando 360 with small valves was originally factory rated at 300hp. After a couple of years of seeing how it ran against some other engines, IHRA decided it was under-rated and upped it a couple of times to the current 320. The result is having to weigh more or the vehicle/engine combo gets bumped up to a faster class. I use to be able to run in L/CM. Now it's I, J and K/CM.
Yes, I'm sure the engine makes a lot more HP. the weight/HP charts show something around 400+. I never had it on a dyno. But all the Stock class engines make more than their rating, especially after doing all the allowed modifications. It's actually just a reference number for classification. When Stock was first started, it was probably pretty close to the actual numbers. Now they allow much more duration, electric water pumps, low tension rings, etc. as well as other little "tricks" that can pass tech.