This is what I use to control my spring brakes. http://www.anythingtruck.com/Merchant2/merchant.mv?Screen=PROD&Category_Code=HTP-AIRB&Product_Code=060-065104
Read up on shuttle valves a bit, still don't get how they can function as a relay ...but the R12 works great to control spring brakes.
Glad to hear you are off the road....don't spend too much $ on air lines....they are usually surprisingly inexpensive.
Make sure you block the suspension as well as scotching the wheels. Air suspended buses drop hard and fast....in case you haven't been told that a million times already.