Read why heatercores are the best for your setup.
Heater Cores have many advantages over any radiator you can buy, that's why some places including D-Tek and DangerDen have started to sell them. When combined with a shroud, so that the air pulls thru the entire core, you can achieve the best performance at the lowest costs.
You can buy a heater core without barbs, and put them on yourself, or buy them pre soldered for a little more expensive price.
You can also use 2 shrouds, one on each side, to do a push/pull configuration. This config has 1 fan pushing air through the heater core, and 1 pulling. This supposedly allows for better temps, however I haven't tried it yet.
Heater Cores have very dense and a lot of fins. They perform so well because of this and the massive surface area. This helps dissipate heat very fast and efficiently.
Some popular heater cores includes…
-86 Chevette Heater Core, its 6x6in cooling area, and about 6x7.5 total size, and 2inches thick which is around $18.95 to $28.95
-89 Camaro Heater Core is another good one, maybe better, but it's a little bigger. It is 7x7cooling area, and 7x8.5 total size, and 2iches thick and costs around $18.95. Both of these are made of copper with aluminum fins for best performance. You need to find a core to fit in your case, but the 86 Chevette core is the smallest non custom one that I know of.
There are quite a few other ones that you could get, some are aluminum and some are copper. It is best to get one based on what your waterblock is made out of, to prevent corrosion.
I hope this has helped you understand a little bit about heater cores, and why they are better than radiators.