Perhaps you can get some new Amal carburetors? A long time ago,about 41 years ago it was common to use Amal carburetors on cars,I put 4 x 28 mm Amal concentric carbs on a 2 Litre Triumph TR 3 A. Amal had a form that you filled out,cam timing exhaust,valve size etc and they supplied the carbs to me as close as they could get.It was a huge success,more power,better fuel economy,(Much better)I never had to tune them once,they got them as near as possible dead right,they sent them to me in NZ.Possibly they were 24 or 26 mm,I forget exactly.I see Amal are still in business,I wonder if they are still as efficient and obliging these days.For a typical 2 litre engine say 6000/7000 rpm they are probably as good as Webbers but at a fraction of the price,and you will be buying British!! David