I had a 40mm DCOE 18 on a B20 with a Lynx manifold. After a few tests, lots of money on parts and some conversations with Daniel at Weber Performance I ended up with this. It was great, just awesome to drive after the carb and the tuning. It was a stocker with a good (standard) exhaust system.
If you do not yet have a carb, just get a new one from Daniel and he will jet it for you, better than getting a second hand one then spending $400 on parts for it - I know from experience.
You will also want to look at a fuel injected throttle pedal and a cable link for the carb. Forget the linkages, they are trouble, clunky, loose and lots more moving parts. Forget the choke cable too, if it is tuned correctly and you know to go easy for the first few minutes in the car then it is a complication you can avoid.
Depending on car, a 144 will take the K&N filter as pictured with a little modification for the steering shaft, also the ram tubes, tiny little dinky ones, will need a bit of die grinder in the air filter.
I found the 40mm was fine for running about town and the occasional burst, if you are going past 5000 RPM more than once a month then maybe more is required, Daniel will know. There is also the bragging rights of having a 45mm DCOE on your car, not sure how much faster that makes it though...
Most of the parts listed below not in the last column are on a shelf here and for sale too.