How to upgrade Arduino UnoR3 clock A little background:

I need to generate a 40KHz frequency as accurately as possible.

(One of my other posts is here: 
Stable frequency generation)

My code is solid- I'm using an Uno R3 and generating the most accurate frequency I can at this point. The only way to get a more accurate frequency is to upgrade the ceramic resonator to a crystal oscillator.

So, my over-arching question is: How do I actually upgrade the ceramic resonator to a crystal oscillator? 

Things I'm considering are:

Is it worth it to actually upgrade my Uno R3 - and is it even possible? Is there a clone that drives the ATMega328p with a crystal oscillator that I could use instead? Is there simply just a better model for this application?
It's really easy to take an ATmega328 chip and wire it up on it's own.  There are even instructions on the Arduino site on how to do it.  Take a look at http://www.arduino.cc/en/Main/Standalone .

You could even pull the 328 out of the Uno, add the crystal and a few caps and then program it with the Uno board.  I've done this a few times myself and it worked just fine for my needs.