Nice job on the trailer there mate!
I think the TI is about 4' longer, so you'd have to lengthen the drawbar as well as add the rear extension. I'm waiting for a couple of quotes for a custom trailer, but I won't be surprised if I have to reconsider the 880GA.
The AI is 16'. The TI is 18'6" so it's only a 2'6" difference. When I modified that trailer I had the TI in mind. I am planning on carrying it as is. The overhang shouldn't be an issue.
I like your design for the trailer. I am on version 4 of my AI trailers. A couple of ideas I have found useful:
1- leave a space large enough to be able to fit through between the bow and the towing hitch. Makes getting around the trailer a lot easier.
2- Standard full width blue poly trailer slider strips (seen at the rear in the pic above) work better than a roller. A roller can distort the hull with the weight concentrated over such a small area.
3-a fixed drop down jockey wheel saves a lot of time.
I got quotes to copy the 880GA Easytrailer from two of our local trailer manufacturers. Both quoted $1500 -nearly double the cost (and both had inferior wheels).
The 12" wheels on the 880 are 110km/h rated.
It wouldn't be too difficult or expensive to extend the 880 to fit the TI IMHO!