I've been doing some homework on these weber dcoe carbs & tbh I'm still not 100% sure it's going to work on this project at all really. It's a bit late now, but I'm still going to run with it. It's only money
So, what I do know is that the twin 40 dcoe's did work well on the 2ltr fiat engine. Therefore, one single 40 dcoe carb should work ok on the 1ltr Vtr engine, but the Vtr engine rev's higher. A hell of a lot higher.
This is my problem, the chart shows that I'm gona need a huge dcoe to accommodate the choke that's needed to feed the engine correctly at 10'000 rpm.
The 40 dcoe will/should feed it correctly up until 5000rpm (34 chokes "I think") It then runs out of puff. Ideal for getting it running & testing but..
Knowing this I was looking for a bigger dcoe, a 42,45,48,50 even 55's weren't out of the question. I then found the RX7 jetted 45 dcoe & was made up. It would fuel it correctly to around 6500rpm which I was happier with.
I'm still looking

for a bigger carb & missed out on a pair of 48 dcoe carbs last night. I messaged the seller about what jets & chokes were fitted but no answer so no bidding. Over £400 they went for
I've since read that the older Italian cast weber 48 dcoe's only accept 42mm chokes max. The newer Spanish dco/sp are capable of running up to 46mm. Maybe a blessing in disguise, £400 for an extra 2mm in diameter. (The RX7 45 dcoe I have has 40mm chokes fitted).
Phew, close shave in my book.