ok so i am assuming the e-31 head is the best head out there for z's right? well i popped my hood of my car to just take a look at the engine and i looked at the lower part of the head and theengine block it was a L24 i saw which was right and then the head was e-31 head and was already on my z?... was that stock or did someone else put that on? and the head cover is unpolished aluminum

Well, I guess it depends on who you talk to if it's THE best, but what's good about it is if you put it on a 280 block the compression goes up. Down side is the valves are smaller than later heads, but they can be changed. Since yours is a '71 the head is more than likely stock.

so then if its stock then by shaveing the head would make it like the performance head correct? also is it worth working on to get it to be like that?

I always thought the newer heads were better like the P90's and N42's. as they had better flow and bigger valves