You will have to give Ben a call, i know hes not cheap but i would think his works 2nd to none and he knows his stuff, not only works on Renaults his portfolio is great having done stuff for FIA motorsport and other top end competors.
He will doing my cylinder head over the winter months along with a re map, as i also own my own company i will be doing his Mk1 fiesta XR2 welding work so its a bit of a labour trade off.
My back ground is over 12 years working on Aston Martins so i also know my stuff.