My original washers were ally and fixings M6 csk stainless. Look on ebay for "countersunk washer aluminium" or "countersunk washer stainless" the 'turned' ones are similar to stock.
Radiator pipe is #6 cut down
http://www.rimmerbros.co.uk/Item--i-GRID000433 as per the original instructions.
Though, the side branch (that goes to the back of the car to the header tank) could do with being positioned higher on the tube to aid prevention of air in the top of the rad.
Someone on here did just such a mod:
radiator-change-t3207-15.html?hilit=radiator pic of it on this thread somewhere.
SAS