After my hdd bit the dust nearly a year ago and reading this thread for months, panicking about what the best solution for a flash memory mod to my 5.5 would be, I've finally gone for the Tarkan bundle so I can use SDXC (and CF if it ever becomes a cheaper option). The SSD route seemed too wrought with possible problems (plus the prices are ping-ponging all over the place).
Anyhoo, this leads me to a question I hope someone can definitively answer for me; namely, once the Tarken board is installed will it allow me to use a thinner 30gb rear plate (or the 30gb iVue). I seem to recall someone stating that the jack(?) didn't line up very well? I'd be really grateful for any advice. After waiting this long (and using my Galaxy Note as my main player) I'm itching to get my 5.5 back on it's feet.
The answer to this is yes, I have done it many times. If your iPod is a 30Gb unit when it was first created, then transition is going to be very smooth. Just pop the Tarkan board with the cf to sdxc converter which you initially loaded with the sdxc card, connect your back plate as usual with the jack and battery connectors, close the lid and voila you are done. The reason why the tarkan works is because it mounts the sdxc card at the top when your iPod is facing the table, the other one I tried mounts at the bottom of the cf adapter and steals a good 2 mm of space.
If you had an 80 gb iPod initially, then it becomes a little bit tricky, although DMinor did mention that it works, I have always substituted the 80 gb jack with a 30 Gb one when installing a thin back plate, call it esthetic; I just like a well finished product. ;)
Hope that answers your questions.
P.S.: Don't forget to install the iPod firmware and test the jack and line out dock before closing the back plate, else you'll have to open it up again and you might risk to scratch it if it was refurbished.