The engine is certainly tunable but you have a heat control problem. Big boost is not a good idea in general so you need to go down a more conventional tuning route first.
The car really comes alive with a standard uno turbo engine, at 150-160 it is quite formidable. The answer is not the power but the wonderful turbo torque coupled with a fairly light chassis. If you can keep the lag down it really is good.
So my recommendations - get the head sorted first to get the gas flow as good as it can get, concentrate on the exhaust side when it comes to the valves, the better the exhaust flow, the quicker the turbo will spin up. The better the overall flow the less work the turbo has to do plus you can run a higher static compression ratio coupled with regular boost and still get the power upgrade.
The Mk I Uno Turbo inlet manifold is nice because the inlet tracts can be dismounted and bored out - the later Mk II manifold doesn't allow this. The throttle plate needs enlarging too - as far as you go if possible. Without this change the power is limited quite severely.
In full race trim we've had these engines run quite monstrous power outputs - between 350 and 450bhp depending on how safe we wanted to run it. Sadly this was only on the dyno. At 450bhp we had a big cooling problem so we could only use it for quite short periods. I'm not suggesting you will get anywhere need this, the cost is formidable and it needs a lot of care that precludes it from regular road use.
The one road car we built like this ran just shy of 300bhp but it needed a fairly big turbo coupled with some trick boost control that actually wasted a lot of the possible boost. If you look at a performance island map for the turbo what we were doing was using the shallower part of the performance up to about 1.5 bar and then ditching the rest in a controlled manner. A regular build is going to need a smaller turbo otherwise the lag will be a pain and the boost when it finally arrives, very big, more than is wise.
If you want to keep the standard engine management you have got a big struggle on your hands - anything more than about 130bhp means you have to use a 5th injector and a boost switch. Personally I'd rather invest in a proper programmable ECU and some mapping - if you've spent all that is necessary on the engine there is no point in skimping on the electrics. The downside of this is even more expense.
If you're on a tight budget then keep it simple - get the head sorted, the manifold sorted and make sure the boost control switch goes to a full 1 bar instead of 0.8 as most of them do. Get it through a rolling road setup before you use it on the road as you need to know it is fuelling properly. The injectors on the those engines are prone to seizing if not used regularly which can do immense damage - a proper controlled run will catch any problems and give you a chance to get it working the way it should and better still a way of knowing what you've got instead of just guessing.
In terms of your engine bay you need to find somewhere sensible for the oil cooler and the intercooler. The usual trick of just squeezing them in is just killing the power of the engine. By all means put the oil cooler down by the left hand duct but if you do that the intercooler needs a supply of fresh cold air and I think you'll soon realise there isn't one. You can put the intercooler down there but you still have the same issue with the oil cooler. Personally I think the intercooler is the better choice to position there and the lesser of two evils in terms of what the engine can cope with.
A bigger intercooler (try a Lancia Delta HF turbo unit) helps as does a bigger oil cooler simply by increasing the radiative surface area. Try taking the inner slats out of the engine cover on that side to improve air flow out of the engine bay. I also seriously recommend upgrading the radiator up front as you are going to be producing a lot more heat than a standard X1/9 and you need the cooling capacity.
Finally the standard Uno Turbo cam profile is pretty good but (and I've not tried this myself) the stock 1500 european camshaft is better according to a lot of the home tuners.
