i'll try sum up a few points that might be relevent but might not depending on what your cars spec is..
Steering..
i had PAS on my valver so it had to go and i had to fit a non PAS rack from a Clio RN or something.. i also have to change the bottom section of my steering column to reach the new rack...
Brakes..
i had ABS so have to rip it all out. i cut up the lines and fitted some T pieces after bending the lines into position. it looks like a 4 year old did it but the breaks are solid and it got throught the old MOT.. brakes are better than my GT turbo
Engine
it will go in but you should get rid of the gearbox mount and use the GTT's gearbox mount by drilling a hole into the subframe. get some new engine mounts as the old ones will be w**k, i got some Pearl diesel mount as there stiffer than gtt ones.
i made a real pigs ar5e of getting the wiring done but its really easy and some help from some people of the RTOC and i had it going..
some things that you need to think about are the header location, intercooler location, swirl pot location, fuel pressure regulator location etc.. i had all sorts of ideas but you just dont have the room and its all jammed in. a gtt exhaust WILL not fit unless you have a Sidey or extend the gtt a few inches.. use the clios gearbox so you can use the speedo and steer clear of the gtt drive shafts as there to short.
http://s12.photobucket.com/albums/a213/gurnachild/clio%20turbo/?start=20
that my photo bucket so you can see some pics.. i've scrapped the front mount idea for now and that was the first fitment of the engine and running in efforts.. im now going into stage 2 which is getting it looking class.. i just can't be bothered tho