factory round mirrors?

[68chevyLQ4]

I just got my new project. 68 with 2001 6.0 lq4 engine and 4l80e trans. Anyway. It had some ugly mirrors on it. I want to put some of the round stock style mirrors on it. The truck came with the round mirrors originally. I can tell because they did a poor job filling the holes when they painted it. Do i just drill the holes out? Doesn't look like the new replacements from LMC have self tapping screws. Do the original holes have threads in them? This is my first 67-72. Ill be asking a lot of questions lol. Thanks!!
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