You make it sound very easy, if only it was as easy as that.
To rebuilt an engine, its engine out job, no ifs no buts, anything other, like rip the head off sump off( ever tried that on a GTR?). Give it a light hone and new rings and bearings and she will be out very soon again .
To answer your question GTRGoddy, yes you can do it yourself as long as you have some exreriance or have someone guide you. You need to pull the donk out, strip it and carefuly check and measure everything, replace anything that is not within specs/worn.
Even the most basic rebuild should include, rebore the block, new pistons and rings, crank checked out and if need be regrind it, new bearings and a new oil pump. Have someone service the cil head and new gaskets, timming belt, tensioner and iddler .