Yes, you can use just the selector weight / lever, I used A2 one (6X0711051) from the EWQ onto the MAL gearbox.
Thats great i took loads of pictures so will share a write up , with the gearboxside mount i used the a2 one with a spacer and a cut here and there . Drove up the road and all seems well. Thanks for the help guysYou could always swap the weight from your old tower to the new one?
The slots are in the section that fits into the lower housing within the gearbox, so probably just for better lubrication, as long as the diameter is the same then either assembly should work.
If in doubt try them both and test before connecting everything up.