O young Lochinvar is come out of the west, Through all the wide Border his steed was the best.
8 is WRONG.
"Wrong" is too categoric here. Actually it's a plausible alternative to no. 6, which I've marked as correct. But seeing the line as having four anapests with a missing first unstressed syllable("[-] oh YOUNG | loch in VAR | is come OUT | of the WEST")is, I think, more plausible than reading it as dactyls with a left-over strong beat at the end:" [Oh] | YOUNG loch in | VAR is come | OUT of the | WEST "