[vectorit]

I can see now my confusion to your Q, since the #2 part you refer to as plastic is actually cast metal on mine.
I am thinking that you might not be in the proper key way on the metal piece sandwiched inside #2 and the turnsignal switch.
This piece of metal is a thick funny shaped part, that has a groove on one side that has a key way in it. That groove is for the #1 part to set in, and the key is to correctly clock the turnsignal switch/lever. It also serves as the anchor point for the turnsignal switch mechanism. Once you have that piece in the correct keyed position, you would then fit the turnsignal switch on top of it, then fasten it down with the three phillips head screws. Doing that will snug up the assembly, closing the gap in your picture. Once you have done that, then you would place the roller bearing over the shaft to where it would settle in the middle of the turn switch. Then the plastic turn switch cancle and horn contact.
Yes, #2 has key ways for the #1 nubs to pass through, but that part I refer to above is what sets the correct clock position of your turnsignal switch. Not #2 since once you fit #2 over the nubs through the key ways it can clock in any direction.
Looking at the gap in your picture, it could be that step that you are not completing?