of the few 4 strokes i've done timing chains on, I fish a wire down thru the cylinder opening, get your chain on the bottom gear, pull it up thru with the wire, slip the top gear into the chain and then onto the cam, replace bolt, all with the timing marks aligned at TDC
and the auto tensioner removed, < push the tension button in and tighten the little holding bolt, install it and loosen the bolt, it will spring out and tension the chain, and continue to tension it as needed, as it is spring loaded
and be sure the chain guides stay in their respective slots down inside