Tricky, I bet you are wondering why
a single 120 rad won't really improve anything (possibly make it worse actually).
The reason is, the liquid cooling system is just a complicated HSF. Instead of heat-pipes moving heat from the base and into the fins, you have water moving heat away from the block, and into the radiator. A single 120 rad doesn't have much more...if any more surface area than your TRUE currently has, and therefore, likely cannot transfer any more heat than your current TRUE.
A 120x2 obviously has more surface area in the fins to transmit heat into the surrounding air.
Honestly, although people keep saying "D-TeK Fuzion v2", you should still be able to get the original Fuzion still, and hopefully save a few bucks. You could also try scrouging for one used off of the for sale forum.
I don't recommend Tygon tubing. Why? It's expensive. From what I've read, Masterkleer, and others should work perfectly fine.
Liquid: Find some distilled water, add 1 or two drops of PT Nuke
And be done with it. Easily the cheapest liquid coolant available.
Before you buy, seriously spend a few nights on this board, reading the faqs, how-tos, and other people's questions. It's what I've done, and I've learned a lot.
Oh, and Thunder? Tricky wants something that's an improvement over his lapped TRUE. He isn't looking for sub-ambient. He is however hoping for more than just a mere 5 degree difference in his load temps to justify the added expense of the WC system. Ideally, I think he would like to get his load temps down to 62 or 60, if it's possible using system relying upon ambinet air, and on a budget.