No argument. Plus the different RPM peaks makes me thing something is going on, as I mentioned.
Could be they rated it after the peak when it was dropping so the '71 340 in effect made 275@5000 but 285@4800 (the same peak as the later low comp motors). So maybe the net rating at 5000 is 5 hp less than the '72 340, but the actual peak is at 4800 where it makes 10 more? And because they listed the gross peak at 5000 RPM for the '71 340, they had to stick to that RPM for the net rating?
200 RPM difference seems awfully small of an window to drop 10 hp, but maybe?