Hi Filipe,
I've had a pair of 40 DCOEs on my TR4 for over 25 years. There is little to wear out on them and they worked well for me on the street (the car is presently not on the street, it's being restored). It's engine is moderately modified with increased compression, oversize pistons and liners, oversize valves, header and sport exhaust, and it is getting a new performance cam soon. Without these mods, the Webers would give little improvement by themselves. The whole idea is to get the engine to breathe better, and it takes a package of modifications to really get the best performance with these carbs.
As others have said, the strength of Webers is high speed performance. They can be tuned for just about any situation, though. But, an SU in good tune is likely a more flexible, all-around street carb.
You cannot use a vacuum advance distributor with DCOEs (but you can with some downdraft Webers). You'll need to convert it to strictly centrifugal advance. This is possible with the stock distributor on the TR4, and my car ran fine with one for years. I'm currently installing a dual point Mallory system, to replace the worn orignal dizzy.
I'm not sure the correct setup on your car, but I would think that using just one carb, a 45 DCOE might be a better choice.
Installing a Weber, you really need to hook up with a local tuner who has a dyno and a pile of jets for the carb. There are many different jets, emulsion tubes and venturis that can be tweaked to get a car to perform. That's the most important part of the installation, setting up the carb to your specific car. Ideally, a tuner would just swap jets and then test the car, arrive at the right setup. Then you are ready to go. At leat until you change something else, such as adding or changing a header, then it's back to the dyno!
Trying to select jets, etc. by trial and error will make you crazy and buying the various sizes of each to do this sort of experimentation will empty your wallet!
A lot of folks have talked down SUs and talked up Webers over the years. Truth is, the SU is a good carb and has a lot of potential, if you want to play around with tuning it. There are larger SUs, too, if that makes sense with your car. Webers are good, too, but use a different approach to metering fuel and air into the engine. There are good books regarding both carb styles and a ton of information available, including recommended Weber configurations for specific engines. You'd do well to track down some of these books and read up before making a final decision.
Cheers!
Alan