There are two Weber Carbs that are popular with Spitfire owners; DGV and DCOE. Also available are DGEV (DGV with electric choke) and DGAV (DGV with water choke).
DCOE carbs are sidedraft, meaning air goes into the carb from the side as original SU’s. DCOEs are higher horsepower carbs but do require much more tuning. Single or dual DCOEs are available for Spitfires.
DGV carbs are downdraft; air comes in from the top like the Zenith Stromberg carbs. Although they can not achive as high horsepower ratings, they are much easier to tune often requiring no modification straight out of the box.
See this link for photo examples of these carbs.
Teglerizer’s Weber DCOE Pages
Paul Tegler built an exceptional page with huge amounts of info on choosing, installing and tuning Weber DCOE carbs. Also includes DGV info.
The page for general set up Weber carbs. Not targeted to any specific model carb or car.
Weber Carb Jetting Table
Jetting table for all major Weber carb models and the cars that got them
Advanced Performance Technology
Sells parts for Weber and most British carbs
Emissions and Crankcase Ventilation
A study and fixes for emissions removal
Oil blowing from Dipstick?
This page explains why and the fix when fitting DGV Weber carbs.