To be fair, there was (is) a major rift in the LP over the correct response to 9/11. There was the political isolationist, anti-nation building crowd that said "Told you so! and wanted to pull US troops out of foreign countries" and the crowd that wanted a swift, vengeful response.
I never heard anything about Browne wanting to employ letters of marque, but I suppose it wouldn't surprise me terribly, although I note that those were traditionally given to privateers and I can't really see how they would be useful against Iraq or Al Qaeda, given the obvious lack of sea battles in the war on terror.
Granted that such Letters are normally given to privateers but Harry's point was that we should essentially place a bounty upon Bin Laden and send bounty hunters after him. Exactly how these bounty hunters were supposed to enter Afghanistan while the Taliban maintained control was never explained to my satisfaction. You will have to admit though that such an approach is in alignment with that portion of the libertarian party that believes that the government can accomplish nothing as well as private enterprise.
I don't doubt that there is some disagreement within the libertarian party on the proper response to terrorism. That's why I tend to rely upon things like their party platform or statements from nationally recognized leaders such as Harry Browne.
Speaking of their platform, what do you think about their position in favor of free and open unrestricted immigration?