I've done one. I've not driven it further than the end of my drive as it needs an MOT and a map, but it's all there.
My car is a MK1 by the MK2s (having owned 2) are extremely similar. Does it require cutting and welding? YES. Plenty. The sump hits the subframe on the O/S and you need to remove a LOT of material from the subframe and build it back up. No-one does off-the-shelf mounts. I've used 2 MK4 golf N/S mounts to hold the engine either side with mount adapters in there to make up the gaps. The dogbone mount is a difficult one. I've done my own bar and moved the mount point. This all sounds simple in words, but it's very time consuming when you get to it.
The real advantages that you get are: An engine setup to run boost with a bottom end to support 270-280 lbft, and a gearbox to support 350bhp / 350 lbft. Whereas an F4R lump really stuggles with the gearboxes that just wont take the power.
I'm pleased with the car, and I don't think I would change the spec much if starting again. But your talking a LOT of hard work to fit it, and probably far more ££ than you'd expect just to get a base 150bhp 20vT running in a clio.
400bhp, you need rods, pistons, recommend a re-bore, manifold (£600+ for anything worthwhile), turbo GT30 ish (£1k+), and tbh 300 bhp is far too much power for FWD and road use, why 400?
4WD would be a HUGE project on a clio if your thinking of S3 gearboxes, and VW transverse gear is not a good way to go (all haldex b****cks). You'd want a complete scoob or EVO (which has been done BTW) setup.
