Not sure about a 172. You probably have to open it with a multi engine land for it to be of any use. Plus, as I have found, single engine ATP examiners are hard to find.
It really was a simple process. Get your TRTO/FTO on board early on and they will help.
I'm not sure if you need a letter of verification of your licence from your own CAA. I got it to be safe, but looking back it may only have been for an FAA licence on the basis of my JAA one. Needless to say don't go down this road or you'll forever be going round in circles checking validities.
A final note. When you go for your Cx ride have all your logbook totals to hand. Including cross country, instrument time, night etc etc. you'll find a list in the far aim I'm sure. They ask for some totals that we generally don't pay attention too.