I was going to suggest chemical metal too. It's what i used for the injector holes on my throttle bodies.
I found the putty type works alot better than the stuff in a tube.
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My Build Diary -
http://davesroadster.blogspot.com/
*updated 7/6/11*
Best bit so far: Getting it running
Worst bit so far: Cutting steel for wishbones and engine mounts.
Most annoying bit so far: Generator packing up half way through welding.