Masonry chimney too short for Oslo...need to increase flue height

We are chasing an exterior wall, clay flue masonry chimney with insulated 6" single wall SS pipe for a Jotul Oslo that will be rear vented.
Measured from the cleanout tee, I only have 13' to the top of the clay liner sticking out above the crown where the plate and cap would be.
I have seen the Extend A Chimney equipment and similar setups, but I was wondering if there is just a top plate that the single wall can terminate into and a 2-3' peice of insulated double wall can be added to for a flue height of 15-16'? I assume this arrangement will keep the inspector happy instead of having 2-3' of single wall hanging out up yonder.

The chimney already meets the 10-3-2 rule (low roof pitch), but since the top layers of brick are deteriorating we are going to have them repaired this coming spring/summer and will have the masonry height brought up to the functional flue height. We would then just add new single wall to complete the project. The double wall would not go to waste, as I am going to eventually need it for when I put a stove in the shop.

The Selkirk adapter seems pretty straight forward. What is the appropriate way to install this style? Do I just use a regular top plate that wraps over the edge of the clay liner, then just drill corresponding holes in the top plate and bolt them together, put a rain skirt on and Voila?
Since I have not yet purchased any of my chimney supplies, I have no idea how strong some of the other sheet metal components such as the top plate are.
Is the top plate typically sturdy and rigid enough to support the double wall on top. I would expect that if I put a 48" section on top, supports could be necessary.

I visited another local shop for fun and they happened to have a Metal Fab single wall to double wall plate adapter sitting on a table. It gave me a better understanding as to fit and how the assembly would work. Things became a lot clearer...so I decided to head to the other shop and lock into the last matte black Oslos they had in stock.

Now for the fun...snow and extension ladders. I might have to watch Christmas Vacation before I dive into this project;-)