You may need a little more pump, but there are a lot of radiators that have 1/2" copper tube in them with fins that would cool the water a lot on it's way back to the bucket. If you set it in front of a normal fan so it had air circulation it would probably help a lot. Make sure it has big tube so it doesn't increase the pressure drop to more than your pump can handle. Your system is so low pressure you could get an oil cooler or transmission cooler from the junk yard. clean it out with solvent and use that to remove heat from the returning water.
I follow your grief about the TIG torch I can say I do have the CK worldwide flex lock and it's a water cooled flex lock it's a FL 230. The Tig torch you have is the Nova roto lock and it comes with two heads and number 9 and a number 17 and I always how well they worked hearing from you that they get hot really fast at 75 amps just tells me it's a POS. Me I started using the wp series Chinese made TIG torches and then I found getting my hands on a CK worldwide and it was a game changer started with a number 17 found the head to be too big and bulky ended up getting a number nine and liking the size then it came to me doing aluminum and my torches would get hot getting the water cooler and a water cooled torch I now have the FL 230 which is a water cooled flex lock I also have the number 20 which is a CK worldwide water cooled number nine but you get into the position to where you can afford it get a CK worldwide...
