If it's a cop-spec or "Heavy Duty" 440, it would have had the following (as per Chrysler's marketing literature):
- Double Roller timing chain
- Moly filled compression rings
- Lubrite treated camshaft (with the same specs as the older high compression 440 magnums)
- Heavier duty rocker arms
- valve spring dampers
- windage trays
- high temp valve seals
- special connecting rods
- shotpeened Nodular iron crankshaft
There were other special features for the ancillary components, namely cooling systems and electrical, but the above apply to the engine itself. These were all added to enable the engine to run for much longer intervals under load, but most didn't contribute to more power.
That said, with the exception of the windage trays & roller chain, not sure if every heavy-duty engine had all of these. Many others have pointed out that could be how the assembly line built the engine that day. I'm also curious as to what the mean by "Special Connecting rods" as that would indicate the six-pack rods, but that would require an extra crank counterweight whereas the cast crank is already a pretty beefy piece so not much room left.
Check out this book for more details too:
Amazon product ASIN 0879389583
EDIT: And the E86 (U code) 440/4 barrel pursuit was also rated at 255HP and 355 lb/ft for 1977 and1978. Given the smog-laden late 70's, they were healthy mills. If you have one, be sure to hold onto it.
