Throttle body bore out

Hi all
Basically I am trying to bore out my current swift TB to 55mm with an oversized butterfly. Rather than gettin a second hand sr20 TB I'd rather have a nice fully overhauled one, and my friend is also doing for cheaper than the cost of an sr20 one.
I've completely stripped down the TB but I cannot seem to remove the rod that goes through the TB and holds the brass butterfly. It was put in somehow, so there must be some way to take it out. Does anyone know how to do this? Any help will be greatly appreciated.

Prob a circlip somewhere
iv got a few spare std tb's if you need one

Cheers mate, I might need a spare if I butcher this one.
I was hoping someone might have done this as I am completely mind boggled as to how I have to seperate it. Please someone help.

I had a quick look at one when I was in the garage
Looks like you just undo the nut take all the springs off, butterfly out and pull it through from the tps end
Without striping 1 down cant realy tell if theres a clip on it

I've already stripped it down that far. The bit where the butterfly was sitting is to wide to be pulled out , and it is also a seperate piece. You can just see that is it joins either side. How it joins, and how it seperates is where I am stuck.