I have just gone through the page referred to by you. And this I thought is what should be done :

1.OSCXCN=0x67
2.Wait for 1ms
3.Check XTLVLD = 1
4. Set OSCICN.3 bit ( to use external oscillator)

I cant figure out why you are doing OSCICN=0x80 - that just enables the missing clock detector.

Raghu