A P8R head would most likely hurt his setup. The 84mm combustion chambers would ultimately drop the compression ratio. Thus the reason jdm b20s with this head have 8.8:1 compression ratios. There is nothing different between the p8r head and the p75 castings. The only difference is the vtec sized intake valves and the 84mm combsution chambers on the p8r, now ask m e how I know
i do think that in order to get 200whp NA on a straight LS your gonna have to have really, really, really deep pockets. Don't plan on making that power on pump gas either. The problem with LS heads is they flow like shit. You can port and port and port all you want, odds are it'll still be outflowed by a stock B16/GSR head. The next problem you'll have is in order to obtain that power your gonna have to rev high. Better plan on a good rotating assembly to withstand the rpms.
You might be able to get closer to your power goals if you plan on running a 2k dollar stroker kit. Again this goes back to deep deep pockets..
My buddies straight LS with b15 pistons and custome OEM geared trans runs 13.9's all day long in his CRX. He has less then 1200 in the entire setup.