Grumpy_Mike:
I don't think you can do it. If you look at the timing you have to be accurate to 100nS and there simply isn't enough time in a 16MHz processor to do that, it turns out to be about two clock cycles. Even in machine code the overhead of reading data and producing those two diffrent waveforms times is too tight.
I think you will have to have a diffrent processor, one that runs faster. Or a very fancy piece of hardware.
Why not have the Arduino write it into a RAM and then use a discrete circuit with a trigger and a precision timer to read the RAM when triggered and bitbang it out all purely using hardware? The biggest, bestest serial to parallel shift register evah. Sure, this is nasty overkill but at least it will prove you can make a nice little bespoke circuit. 