>
>
> I'm transferring at 9600 baud.  Aren't the latter two insignificant at
> such a low frequency?  Over two-inch traces?


No. The risetime and falltime of the edges have lots of high frequency
energy.
If you don't have a SOLID ground between the two devices, you can radiate
like hell.
The resistors are best when located close to the driving pin, rather than
the driven pin, and end up optimal for fast signals at about 100 ohms,
slower signals can use larger values. In your case, 4.7k would be good.
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