Heres a pic of my 20 or 21cc echo.As you can see i did one of the ways you mentioned.Mine is a straight shaft also.I didnt put a keyway in yet and not sure if i will.I put a taper on bottom of hub to match taper on crank.When tightned down it shoudnt move.Not sure if im going gas/glow or not yet.The weight on mine in pic is 2lb,7ozs.The shroud around engine was the stock cooling shroud and i left it on there and bent the edges out a little to promote good airflow around the cylinder.This has domed piston top.Dont know if its better or not.As you can see it has the 4 bolt case with large bearings and seals.Doesnt the poulan have the cantlever crank and no rear bearing.