I talked to some hardware gurus here and since the rails are different it is very likely that you have to swap the rails. I cannot give 100% guarantee since I have not seen them myself though.
Can I ask you a few questions concerning the 5500C appliances.
1. We are currently using 188.8.131.52 in a vm environment - Can I assume that the 5500C operate on 7.4 (or need 7.5 ?)
2. I am lead to believe these appliances are customised for the WG environment - is information available with tech. stats etc.