I made my own.
What do you mean? How far do you want to go? I insulated the plenum using aluminium, loft insulation and gold heat tape.
The M already has cold air induction as the air flows in from the brake duct which is already as cold as the ambient temp.
Are you considering cooling the air with refrigerant?
http://www.ebcbrakeshop.co.uk/info-part-list?make=BMW&model=Z3&spec=3.2 M&year=1998 (R-S) now discs and pads are £298 Ultimax and Redstuff are different ;)
www.zroadster.org