You really don't need a dwell meter or feeler gauge to adjust the GM style externally adjustable point. Here's how my dad showed me to do it many years ago:
Start the car up and let it idle. Then use a screwdriver or allen wrench and slowly start turning the adjustment screw in. Continue until the engine starts to misfire. At that point the engine may die, if so don't worry about it. Then turn the adjustment screw out exactly 1/2 turn and your points will be set.
Then you can go out and buy that tach/dwell meter and see that you will be right close to the 30 degree desired dwell setting.
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North Dakotas fastest REAL GTO
10.10 @ 131 MPH in the 1/4
Hoping to get it back together some year.
www.jandjrepairandrestoration