I use a guy with a garage in the Feltham / Hounslow area. He is excellent and has extensive GTR knowledge (currently uses an r32 gtr as his personal car). I use him for all my mechanical work. PM me if the location is viable for you and I will pop his number across.
SivTech in Storrington. Ash who owns it is a Skyline Specialist, he built a 700hp RB26DETT powered R32. He's your boy.