Update
Ok, so I bought the LPA sights at TSE around March 5th. It was the last set they had.
At the time they also had two sets of XS Ghostring sights for Winchesters with the ramp on the barrell for the front sight. As far as I know, the rear sight is the same and will fit the tapped holes on the new Mossberg 500. The front sight is just the post, so you would need a ramp.
The LPA I got was the SG3M1B banded front sight that clamps on , no gunsmithing needed.
Because of the way the Mossberg is built the LPA can't just slide on like it is supposed to, so I cut a slot in the bandso it could slide far enough in for the front to be even with the front of the barrel. Then I just sanded off te camo paint on the barrel, and rubbed it up with a file and some sandpaper, and roughed up the inside of the band on the sight, and epoxied it. A LOT of epoxy, plus the original clamping system.
On my 870 Desert Recon I have Wilson Combat / Scattergun Tech Ghost Ring sights, and on my older 870 I just mounted the LPA rear sight and the XS front post on the original front ramp.
In use I can't really tell the difference on short distance, and the only real difference is that I can put an improved cylinder choke in the Desert Recon, and it makes a noticeable difference with slugs at a hundred .
Also, check out this link for mounting of a front sight:
http://www.brianenos.com/forums/index.php?showtopic=96928
I thought it was interesting how he just drilled through the barrel and then used the dremel to grind off the screws after. Naturally this wouldn't work so good in a shotgun with screw-in chokes...
And check out Tacord, they have a bunch of Ghost ring sights on their website.