If you want an SU carby, let me know, I'll donate one free to the project. I've got a couple of 1 3/4" SUs, The only thing you need to do is get the needle profile right. If you were running twins or more SUs, you need to go through multiple needle swaps. With a single one, you can actually get away with a nice little trick. You deliberately select a needle that is too thick and runs lean. (whatever you do, don't run it up with massive boost at that stage) and you slowly file the needle down to be thinner in the appropriate section (you can work it out fairly well - the first thickest section near the top is for idle through to light cruise, the middle 1/3rd is for part throttle through to small hills but no boost, and the last 1/3rd is for boost. So in general terms you keep it relatively thick at the top, and take a reasonable amount off the bottom. you basically need to use an ego sensor to get it close.

I haven't done a drawthrough SU on a 1.2 litre four, so I can't give you a ballpark sort of needle profile, you'd have to do the trial and error.

One thing I will mention. Apart from the really ancient stuff, there's two types of SUs that you'll come across. The hs type, which have external fuel bowl off to the side, and the modern 'hif' type SU. ALthough the hif arguably has some innovations that make it a little bit better to get economy, I would not recommend it - and here is the 'why'. Two changes (amongst many) they make is that the needle is spring loaded and 'leans' to the side, so it always rubs against the jet that it slides inside of to change the effective jet open area. This will cause the needle to wear out the jet over about 3 years of use, which will make it get richer and richer as it wears the jet. It also wears down the needle. Worse still, it can 'jam' if you hand file the needle to get it right, so you'd have to run store bought needles (at probably $15 each till you get the right one) Secondly, they have a sort of 'automatic choke' device - which is a metal bracket which holds the jet in place that is bimetallic - two slithers of different metal stuch together. They expand at different rates, so as it heats up, it warps the bracket and lifts the jet a little bit, which leans out the mixture. In other words, when cold it automatically runs richer, and as the motor warms, it leans out to the proper a/f mixture when the engine is up to operating temps. The problem with it (and this experience comes from blowthrough setups on minis, but it's likely to happen on a few others) that heat from the turbo underbonnet can be enough to warp it further, so when it's up and running and spooled up, it leans out, and obviously you'd actually want it to be richer as you feed in boost and underbonnet temps increase as a result of radiation from the turbo exhaust scroll.

Anyhoo - if you want an SU, just let me know (you'd probably get good results from a 1 1/2" SU - a single 1 3/4 on a drawthrough can support over 200 flywheel bhp (not that you'd necessarily want to run just one by that stage) which is well over what you'd be chasing with your setup. - I'm happy to donate a carby, but it'd have to be in a week or two, as they are all trapped in a corner of the shed with a few engine blocks and things in the way.