LEDs 
So let's get this right. Are you replacing the 2D fitting? Or looking to replace only what's inside the fitting? Got photos?
Basically in the current fitting the lamp mount and ballast are together. Like so:

Led light looks like this at the back (as you can see it has its own ballast with transformer and starter...):

The two won't join together as ballasts get in the way of each other, I can modify the the first ballast and shop the box off so only the 4 pins are exposed, if I do this I am guessing two pins need a neutral and live supply, but I'm guessing it has to be on specific pins which I do not no, usually you get a mini adapter like so (you can see on the left the female adapter, again if I had this what pins do the lives and neutral go to or doesn't it matter?):
