[Users] DL380 G5 - Fails to Activate

Hi I have a couple of old DL380 G5's and i am putting them into their own cluster for testing various things out. The install of 3.1 from dreyou goes fine onto them but when they try to activate i get the following Host xxx.xxx.net.uk moved to Non-Operational state as host does not meet the cluster's minimum CPU level. Missing CPU features : model_Conroe, nx KVM appears to run just fine on these host and their cpu's are Intel(R) Xeon(R) CPU 5140 @ 2.33GHz Is it possible to add these in to a 3.1 cluster ?? thanks