'Splain this to me, Lucy.

OK, just got done decoding my '72 Duster 340 fender ID tag. Everything matches from what I can see, except one thing...the bottom row, far left set of digits is "E55", which decodes as "340 cid, 4 barrel V8 275 HP"
Now, I was always under the impression that the '72 motors were 8.5:1 compression, 240 HP from the factory according to all the info I've found to date. Was there some option to install a higher HP motor in these cars, or is the decoder program wrong?