The adapter plate is tapered for 28/32 inlets so that sits on top of your manifold.
Then the carb on top of the adapter. I dont recommend you use this
on a standard A10 as it would only benefit if you used some sort
of fast road camshaft to get it to flow properly.
I always think an early a12 is a nice motor for the b10
and you stash your a10 away in the shed for originality.
Or do what Dodgeman Chris has done with the A14 within an A12 hybrid.

Once re-jetted for your application and if the application is mild/warm/hot
then you can expect the air velocity and fuel mix to be better than a single 45mm
weber for the road as its designed for all round performance rather than top end.
A single 45mm twin weber requires a serious cam to get it
moving and then its a pig to drive in comparison to a downdraft
with more complicated flow path that improves torque.
Its really what is considered a grunter carb where unlike the twin
hitachi which have a delay in acceleration you get instant throttle
response also. Even hillman Imps with 875cc used a single 40mm weber
sidedraft as the 45 takes to long to reach optimum air velocity for proper fuel mixing.