If I remember right when you register it will tell you which club to find the serial number on?  Having said that it does seem weird that your 4 and W are different than the rest of the set.  I will take a look at mine and see if they're all the same or…

I was also between those two.  I figured that the AP1's were more forgiving, which helps make up for my lack of time to actually practice.  I do like the 2's quite a bit but figured the added forgiveness would be better, for me.

it is fairly easy to do, use the tool and unscrew the shaft then you can take it out and replace it. be careful not to force the shaft as they are somewhat delicate. but with a few trial runs you should get it down easy.