The N47 (8/77-6/80)Z is considered to be not as desirable as the (81-83) P79 and P90 heads, due to exhaust liners and inferior combustion chamber design.
The (1981-83) N47 Maxima head is much different. First, it has heart-shaped combustion chambers like the P79/90. Second, it's combustion chambers are about 40CC, even smaller than the E31 & E88. The Maxima head also has exhaust liners.
I'm thinking about slapping an N47 Maxima head on my L24 for 9.5:1 compression, so I've been researching this a bit.
I am not thoroughly convinced that the exhaust liners are a bad thing, since no one has numbers to prove it.