i think the 5 pot could fit but...youd need custom mounts and alot of custom stuff to get it in

new gearbox maybe, all the electrics etc etc

my advice would be to turbo/supercharge the engine you have now, its the same engine as a fiesta st basically and alot of people supercharge those so that could be an easier option (wouldnt imagine space to be an issue in a mondeo bay if itll fit in a fiesta!?) if you want a charged car

but for n/a exhaust, induction kit, remap, different inlet, head work etc etc

a 2.3 conversion would be great in either form, and they can be bored out to 2.5

what kind of thing are you wanting at the end of it? charged or n/a? power? and what sort of budget do you have?