Well i just got in my Type G 3/8" elbows from Danger Den and they are what I needed. They flow better than anything I can find locally and thread in with no resistance at all.
I noticed that one corner was going to hit the water line so I took a hack saw and cut off the mounting bracket on one side of the fan. The cut can be seen in the image below. Nothing vibrates or makes noise with the corner being cut off, so either I got lucky on that or tightened the other three corners up enough for them to hold everything tight.
Now everything fits in the original housing and my Nautilus 500 now cools 4-5C cooler under load.
Words of advice for those following in my footsteps. Order the 90 degree elbows in place of the straight fittings when you order the radiator from Danger Den and they wont cost you anything extra! The Aerocool fan doesn't improve cooling, but does look damn cool at night with the blue LED's.
In closing...
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If anyone reading this tries this or has already improved their Nautilus 500 their own please post up what you did to help others.