yes i have fitted it with no probs its all in the prep pipes are very very tight as you say but it is just about doable there was a thread on it all a few weeks ago and like i said then theres always room for improvement with everything it was a quick pop into engineering place asked the chap if he can make these into that and here we go no real thought or faffing around job done as for the restriction i aint noticed any at all its arguable that it does but if anything it stops all the sh!te from going back up through as there is no filter in it which is summat else that needs to be sorted
another thing i didn't like was how they point the pipes upwards. would be better going in flat IMO
pic of the install not the best pic but 19mm all the way through