from my understanding of it so far, as i was thinking of going 3.0 24v, or 20v turbo into my 2.5 v6 12v 155, the 12v era motors will be easier due to the similarities in auxililarty components and electronics,
but, the fly by wire later stuff, mostly 24v motors, will run fine on the earlier mechancial air flow meters and throttle arrangement once spring tension is set correctly, so well in fact that the last cinversion i read up on had a 3.0 24v motor from 166/gtv i believe, and on his 2.5 12v airflow meter dyno'd immediately at around 220bhp, eastwood garage down cornwall way i think it was, so bang on the mark for a good stock set up straight away!
the beauty of the modular tipo set up, is that luckily for us the donor cars we want are cheaper than sourcing the bits, so long as you find a whole car with everything you want, these CAN be cheaply modified and hugely improved cars,
i hope, sometime next year
plus, they can be screwed together so well, no need to bodge anything in, that you'll wonder why AR didn't build what you've just created.
i went in Kev's 20v turbo 145, it was a great drive, very very well behaved, and just like a factory had put it together, fantastic!
and as langers says, a turbo motor is very easily tuned for more poke, and much cheaper power for pound than normally aspirated, plus the 5 cylinder sounds magic!
best of luck when you get the budget and to grips with it mate, all power to you...