There is no room to be able to correctly wire the nuts (I tried) hence my search for an alternative. The Nord-Lock I used are 3/8" IIRC but worth checking the stud size before ordering. They are widely available in the USA. This illustrates how they work:
My experience suggests:
1. The cheaper zinc plated Nord-Locks can only be used once as the heat affects hardness but they will not allow the nuts to move when they are in place. Once removed replace with new Nord-Locks each time
2. The more expensive stainless steel Nord-Locks can be used repeatedly but are five times the price of the zinc plated steel. Use them if you intend to regularly remove your down pipes.
3. The nuts will require torquing up after two hot/cold cycles but after that they should remain tight.
4. There appears to be no advantage to torquing the nuts up when the engine is hot.
5. The zinc plated Nord-Locks are a 'use once' washer in this application. In other areas, not subject to extremes of heat, they can be used multiple times.
This could be another neat option:
http://www.stage8.com/
Available via eBay not cheap but highly regarded. They would also be excellent to replace the manifold to head studs which also come loose. This is the 'stud' version:
