400 Gross power?

you can also look at the 71 and 72 440 and 360

look at the compression ratio difference between the two years, and keep that in mind when comparing the 1971 (gross) and 1972 (net) HP

in general, IIRC, there is about a 20% reduction from gross to net rating

apply that and note any design differences as above and you will be close

also note that subtracting 20% from gross and adding 20% to net do NOT come up with the same numbers