Not really sure how to tell what it's ported to but by measuring it with calipers the filter side is 55mm and the motor side is 44mm.
I know it was ported and it was done by a professional shop.
The size should be measured at the flap, the filter opening is probably larger and narrows down to the flap. I have a 58, the opening at the filter is little more than 63mm so that's a difference of 5. If you have 55 at the opening your probably at 50 at the flap, so that would mean you have a 50mm TB not a 55. I don't think the 46mm which is the original size on a 06, can be milled out to a 55. I think they can only go to around 51mm, which would make it accurate to say you have a 50 or possibly 51mm TB.
To really know you can take the flap out and measure it for accuracy of what you have.