The 1.4 head surely has smaller ports valves than the 1.8 head? Sorry but I think your going on a time wasting and money wasting way. Get your 1.6 head skimmed, and polished and ported. put some lairy cams in and you will feel a big difference. or drop a 1.8 or 2.0 engine into it. Personnally after more than one person has advised this to you I would seriously think that they are offering you good sound advice.