You only need to worry about the OS and drive array configuration matching, don't be too concerned about the mother boards, back planes, RAID cards being identical. As long as the 2 servers present their storage arrays in the same format and volume sizes you should be OK.
If it was me I would want the RAID arrays to be the same if only to simplify the setup - I cant see that mixing RAID 5+1 and 1+0 (to pick an example) is a great idea. That being said I have never setup a cluster with dissimilar RAID types so it could be possible, but if you have the option now to set it up effectively from scratch then use the opportunity to get them alligned now - it could save you headaches later on.
When designing things like this keep the configuration as simple as possible, as clever combinations of different technologies often end up costing more time and effort to support.
Good luck.