Exactly, I agree... Not sure if your trying to assemble the lower unit with that plastic piece on the lower unit or not, but I find that these two things help alot while reassembling... If you put a dobber of grease on that piece and stick it up into the mid section where it goes it will stay up there because of the friction from the grease... That will keep the shift rod lined up where it needs to be. Secondly, If you put something under the lower carb between the carb and the shift rod, it will keep the rod pushed down so it won't rise up when your trying to put them back together... From there on out its just a matter of "finessing" the two together while someone gently moves the flywheel a little back and forth to allow the splines to match up while your holding pressure up on the lower unit... When it does it will stab up in there when the line up. Enough for you to get the two nuts onto the sides of the lower unit. Obviously , this is all contingent on you having the upper and lower in the same gear position...
