You need an engine piece that contain the housing of self, self starter motor and have to reassemble the engine for fitting these things.
A suggestion for you is to buy an engine from ranchoreline that has builtin self starter, afterwrads you only need to take out old engine, put it in your home and fit the new engine in chassis. Use it till you change your mind to sale the bike. When selling put the original engine back and keep this self starter engine with you at your home.
Simple!