Tandem master cylinder : £105.00 exchange with £50 surcharge if you don't have a RHD unit in serviceable condition to exchange
Four way bulkhead union with shuttle valve
Foot brake warning light within cluster
Various adaptations to the pipework
Actually, you don't NEED the PDWA valve (4 way union with shuttle valve in Alun's description above) or the footbrake warning light wiring it supplies. The factory fitted these as an add on when they converted to dual circuit, but there are much better and more reliable methods available nowadays (saab 9-3 reservoir caps with fluid level sensors fit straight onto the dual circuit master, £5 or less from your local non specific scrappy)
What you will need is the master cylinder itself, 2 bespoke pipes from it to the position of the original 4 way union on the bulkead and a new imperial 3 way union adaptor. If you go ahead, I can make the bespoke pipes needed, supply you with a 3 way and a diagram of how it all goes together.