Heater core / Heater Tap GTV V6 Phase-1

[Alfa166]

Has anybody replaced the heater core on a Phase-1 GTV V6 , looks like from it's location it is a pain of a job. Anyone got any idea how much to replace in parts and labour. Alternatively does anyone know how you get at the top screw on the cover that goes over where the heater tap is . Bottom screw is easy but have no idea how you get to the top screw.