Rick, When you drill the lip on the radiator,You can use a small rubber hose for a stop. just put the bit through the hole in the hose, and let the bit stick out about an 1/8 inch, There other methods, you can use tape on the bit. or erasers. anything that will block the bit from going to deep. You could also use 1/4 selftapping screws, They don't walk like the philps selftapping screws.
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awsum34

Why do people park in a driveway, and drive in a parkway?

Thanks, great ideas, I find a tape flap works great for a depth stop. I still fear cutting the core. Also, I forgot to mention, I am using a stainless overflow tank, I probably will make some brackets like I saw at a recent show on someones ride. Rick
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Rick Menard