The new curved inlet manifold makes a big difference as each cylinder receives the same amount of fuel instead of two being rich or two being lean as with the 'log' manifold. If you couple it with the K&N Apollo air filter you have denser, colder air forced in from the front of the car instead of just having warm air sucked in from above the exhaust. As a result you get a noticeable difference in how the car responds.
We fitted one of the first of these Owner's Club' carburettor and manifold set ups several years and many thousands of miles ago. Apart from washing out the Apollo air filter and re-oiling it occasionally, we have not touched it since it was installed. It is a 'fit and forget' improvement.
Compared to Strombergs it is MUCH smoother and ticks over more slowly, acceleration is at least as crisp if not more so and we have never reached absolute top speed but would guess it is very similar. It certainly cruises at 70mph + with no problem for hour after hour. If you watch any of the videos in the 'Driving' playlist on the Sunbeam Alpine Channel on YouTube you will see how this car performs in daily use.
Apart from not constantly needing to be synchronised like the Strombergs there is no risk of diaphragms splitting (again).
We have this set up on two of our Alpines, on one we replaced a 28/32 Weber on a Log manifold. It is a very good improvement that you will not regret, (your miles per gallon will go up too).
Tim R