Replace the filters too, although everything will have thawed out now, both your particulate filter and the carbon filter will have froze solid, can't imagine that would have done then an awful lot of good!
Be careful when replacing the casings though...I had the same problem and got my replacements from WCW...rang them in the afternoon and the replacements were with me the following morning (great service from WCW)
Although the casings were the same size (10inch housings) the threads on the original ones were on the inside of the casings (Gaps water 4040 setup) the ones from WCW had the threads on the outside of the casings...
Was sorted out ok by them, but there is no standardization with these things, so take care!!
Ian.