I have, in fact the reserve unit I'm getting into is in 170 group. I've specifically asked to go to 521STRE sister reserve group, ie the water team (I think 506?). Sounds like you have experience with 170, could you impart some of your knowledge of the role of regular officer in relation to 170 and infrastructure engineering? Given my previous experience, I'd be very keen on 521 STRE to be honest, but worried you don't get to to be that specific post sandhurst however.
Just stumbled across this thread, I'm looking to join 170 group too. I have Alpha training starting 04/09 at Grantham. I am unsure which of the teams to go into after passing training though!