The Remington handguards in the ebay auction have the following unique/distinguishing characteristics:
(1) Concave high hump profile
(2) Full "half-moon" windage knob relief cut. (Most armory handguards have a "quarter-moon" windage knob relief cut).
(3) A square sight line clearance groove with sharp corners in the bottom. Most, but not all Remington handguards have this feature.
(4) NO fixturing slot in the barrel channel at the rear.
(5) Rough unfinished barrel channel for most of the length. (Armory handguards have smoothly-finished barrel channels).
(6) A distinct 1" wide relief cut in the barrel channel for the front metal clip.
Hope this helps.
J.B.