I think the turbo will be too large, but it may work.

Even though others are talking of using T3's on an A12-A15, this is a very large turbo, and probably wouldn't be well suited to an A-series engine. With a small engine, getting more torque down low, by using a reasonable sized turbo, will give you better results. I doubt that any A-series carby will be able to deliver enough atomised fuel for a T3 turbo's airflow..This would be only ok if you ran a proportionally sized throttle body and fuel injection.

Making the intercooler out of an old radiator is not a great idea. Just use a cross over pipe in the short term. You will have enough carby headaches to fix first. Get an intercooler out of something else. Even a small one will make a difference, do this after you get the engine running.

I read recently hre, thatthe old copper bulb can be squashed under boost, so the solid plastic float sounds like it will help you. The cork gaskets in the carby may not work, but it's worth a try.

So I think your priorities should be:
1. Get the concept to work.
2. Put an intercooler in.
3. Get a larger turbo / carby.

There's a lot of variables, and you don't want to spend loads of money to find your carby explodes into pieces everytime you put your foot down.

Remember with carbies you are more likely to burn out pistons etc. due to bad mixtures. The tuning of the carby to suit the turbo boost curve will be a huge job.
It's much easier with fuel injection because the fuel delivery under the different load conditions is variable. With carbies you are limited to:

1. idle jets
2. Accellerator pump jets
3. main jets

During tuning you will need to make/borrow an air/fuel mixture meter, to ensure that your ratio is good to stop lean-out.

It's not as easy as just making a manifold and pushing compressed air in the carby.

You may have good luck and it will be easy.

Good luck, I'm always happy to discuss my opinions. I've not done a turbo'ed A-series project, mainly due to R&D costs and unknown results.

Chris.