ok a few points:
Turbo charging the MPI would be the simpler ( not easy in relation to carb)of the injecton systems as you can use the original inlet swap out the throttle body for a turbo ( sealed unit, if there is actualy any difference other than it being alloy) off another Rover (almost like for like), pipe the discharge of the compressor through an RS intercooler going direct onto the throttle body. The MPI already has two injectors with others freely available in a veriety of cc/min to match the power, all the temp sensors are there, already has an oxygen sensor, all the wiring and relays are there and the direct fire distributorless ignition coil.
I personaly would use the Megasquirt engine management system as it is freely adaptable to almost every situation. Only one problem I see is the crank position sensor, I don't know if any one has coded the Megasquirt for Rovers unique pick up pattern. It would also be easy to fit a knock sensor. This along with the usual turbo required mods of course.
Big boost high power engines would require very big injectors in relation, causing difficulty in a single or twin injector system to control the low rpm fueling, so medium power increases would be much more succesful
cant see why it cant be done, but it certainly would not be as simple a carb turbo.
Realy got to get this sussed for my project, though I will be using four injectors with a single throttle, similar to below but not the same
EDIT: picture changed
MPi inlet will not fit with turbo ex manifold.
MPi has one-bar map sensor. It will not see any boost, hence will not pull the ignition away. Also will not add more fuel as boost increases.
MPi injectors are already high-impedance 480cc/min items. Bear in mind that despite these, the MPi still has difficulty going over 66hp/litre.
MEMS is not mappable.
Someone has recently figured out the Rover (k-series at least) flywheel for MS
MS will still not perform 'correctly' (ie at 1000 rpm aswell as 7000rpm) on an A-series.
To get round the MPi issue, I'd have a second set of injectors fitted. Then, a 'piggyback injection controller for each MEMS injector channel, such that you can use the signal from the mems (so the second injector is triggering at the right time to prevent charge-stealing) and adjust the output of this injector to add the additional fuel.
You then will need a wasted-spark style (two channel) boost retard system to pull a few degrees off the MEMs advance as the boost builds.
A one-way check valve (eg 'missing link' as used by honda tuners) to prevent the map sensor seeing boost.
All pretty complex all in all!
A BMW or even 7-port head with MS would end up easier and cheaper probably!