I dont see your sketch(Try to post the sketch again), but you'll need to chase down some fairly old cars for their radiators. Most of the newer radiators are made of aluminum, which is hard to work with, youll be pretty much stuck with the size of the radiator whatever the size is.
Also you will have problems with your connections(each and every connection is a leak waiting to happen). Ideal size for cooling inside the computer is 1/4 - 3/8 tubing youll have to neck up/down to be able to fit the 1.5" to 2" inlet and outlet to the radiator.
IMO, you would be better off buying new, or off Ebay(as long as YOUR CAREFUL) you can get deals like this one(at 2.76 right now, dont know what itll finish as):
http://cgi.ebay.com/ws/eBayISAPI.dll...&category=3673