I've done the conversion, and although it is simple in theory, there can be complications. Be prepared to do work on the manual box after you've fitted it, unless you can test it in a car first(unlikely). It felt to me as if my car gained 20KW at the rear wheels with the manual (I had a 4 speed).
Next week I'm having a remap of the unichip, so I'll be able to compare manual to auto Kw on the dyno. There have been some other mods though, so it won't be a definitive test.
I really love the control and involvement of the manual- double de-clutching , being in the right gear going into a corner, and for braking.