I would go ahead and request which longhouse you want. It doesn't mean you'll get it, but it doesn't hurt to request it. I've gotten the longhouse I requested both times we've stayed there, but not necessarily the floor I requested.
I do think the check-in CM's allot rooms by priority of who's checking in versus those who have made a request but haven't arrived yet. Among people who have not yet checked in, putting a request for a longhouse, floor, etc. should be ahead of others who make no such requests, assuming the same check-in time. But if there's, say, only one room left of the type you want, and someone gets there before you and checks in, I think the CM will give it to that person, rather than keeping it from that person based on a request from someone who has not shown up yet.
Usually, this seems to result in at least getting the longhouse building you want if you show up for check in at a decent hour, but it may not result in the floor you want or the exact view. Personally, I've never been disappointed in the Poly, except for that pesky check-out date that they enforce so stringently.
