ARB bushes will give a clunk when going over speedbumps. I would double check the bits replaced first (droplinks as they would give movement in the ARB if not tightened).
Given that its so high on the engine, you will be able to remove the screw and inspect the threads i would have thought (do it when the engine is cold though). You may loose a tiny amount of coolant i would imagine but that can be easily topped back up.
too small for a standard exhaust, i fitted these http://www.ebay.co.uk/itm/2-5-63mm-Stainless-Sports-Exhaust-Tailpipe-Rolled-IN-Tip-WELD-ON-STYLE-/250863162292?hash=item3a689c13b4:m:mQ6HJUFbVVavQZ7T5_wcr5A
Be careful with them, i had to drill one of mine out as they are soft - use plenty of lubricating fluid and hit the socket into position with a few light hammer taps.
Looks like it, OEM part number cross references to here http://www.renaultpartsdirect.co.uk/product/renault-clio-197-shock-absorber-top-mount-kit/
This is the one i bought (they are sided)...
Brill, coincidence but the day after you posted this up, a set came for sale through a mutual friend for £650 - excellent saving over the normal RUK ones. Although these were the Nurburgring edition ones, so obvious they came from a corsa.
I bought this one as an alternative to OE (Febi) , just seen its down to £11!! Assuming due to amazon prime day
https://www.amazon.co.uk/gp/product/B00CD3VXA8/?tag=clio197-21
Changed both of mine for Febi items, done about 12 months / 8k on them so far.
For me a decent branded aftermarket part will always trump a genuine item where there is a decent cost saving to be had.