Interesting to see a converted single carb head, how did you seal the manifold given there appears to be no meat in the joins at 4 and 7 oclock...
Your carbs sit nicely in the frame space, almost room for a still air box...
As you mention everyone loves the look of GP or TT carbs, but they are not the easiest carbs to live with in a twin carb set up, probably why the a65 spitfires had them for such a short time. Ok if you dont mind fettling but for a bike under factory warranty, you can imagine the customer complaints.
My own twin carb (TT) set up is on the twin port '55 head, so much easier to manage and for a race bike twin carbs are constantly being checked along with everything else and the TT carbs are great with Methanol.
Now a 358 would be nice to have, but probably useless on a sidecar. Needs to go on an A7 race bike to give those gold stars a run for their money.