Good Work! I've been thinking about a similar model and have collected some relevant photos. I could not find any record of a four-seat T26 fastback. Except for this recent barn find designed by Pierre Saoutchik. It was done on the longer Record chassis and the other fastbacks were apparently done on the shorter GS chassis.
Fantastic! You're making it look too easy - this is really challenging work. It's starting to have a bit of a Prowler vibe. To make it more practical, you could use a perimeter frame, drop the seats as much as possible, and bump out the firewall for leg room (see a Jag XKE).
If you want to strengthen a join, apply a fat line of regular superglue along the inner side of the join, then cover with baking soda. Only do this where you won't want to remove any, as it sets up almost like stone. I do this quite a bit, since I only build customs myself.
You're brave doing a custom for your fourth model. Good start with the new trunk area. A candle!?! More bravery! What kind of plastic did you use? I try to make sure body parts are very well attached and supported I often use super glue plus baking soda for an easy reinforcement on the back side where it won't show. Helps to avoid problems when I'm cutting, shaping and so forth.