swapping the 2E3 for a Weber twin choke is not going to release many bhp as a sole modification. Used in conjunction with modifications such as some decent headwork and a lairy cam, then it will really work well and can give just as much power as twin 40s on the right engine.
ive paid over 650 quid for my twin 40s, including manifold, all pipework, jet and belt changes, but they are awesome, but will, no doubt cost a fortune to keep in tune, but worth it imo...