The 2400bps receiver doesn't use a crystal. You should buy the 2400bps receiver (http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?action=post;num=1282815280;title=PostReply) NOT the 4800bps since the 2400bps has a tuning slug on the back of the board.
And if you were to change the crystal of a receiver, remember that the crystal will not necessarily be 310MHz for a 310MHz receiver. A typical 433MHz receiver crystal is 13.2256MHz and a typical 315MHz receiver uses a 9.5094MHz crystal. So you would need to carefully select a crystal that would give you a 310MHz output. But I'm not sure it's this simple, and the right crystal might be hard or impossible to find.