Forget 2.4 conversions as to costly, it is up to you but YB will give loads more power if you want, over a pinto, due to head design(16 valves).250 bhp out of a turbo pinto and clean emissions is relatively easy but costly.
If you have a aftermarket ECU, then software can be written that will achieve low emissions and big power, and just a CUT switch for the power at test time.
All turbo's have their boost controlled, by interupting this circuit you can drop the power to no boost at all.
You are looking at big valve head, different cam, aftermarket ecu(I+F), plus all the turbo install bits, either a T25/28/3 would suit.
I think your biggest problem is finding those bits ?
With the ecu you can have one with alternate maps, so you merely turn it from a full power map to a nothing map(no boost!).
Another major consideration is to get a ecu that people are familiar with where you are, so they can map it.
It is going to cost more than buying a cossie in the end so would this not be a better option, or is the test/law stopping this ?
tabetha