It might get a bit tight Geoff, after getting a nibble you have ~100uS to get back to the getNibble() function. If you don't make it you are out of sync again. I'll have a think about the timing but it may be better to put that code inline, at least that will save a function call.
You do say it works, so I presume I'm wrong on that point.
I'm not sure newbee_2 is using my code.
One thing I/we didn't think of is that presumably the PC still needs to see the preamble as it doesn't know all this is happening. So after we get in sync we need to send those 6 bytes.
Rob