I thought the 10ga shotgun and 12ga slug barrels were the only ones that require a different forend, that said, even some forends need some modification to fits some rifle barrels, the forend studs aren't identically placed on all rifles, they apparently mis-position some of them when they weld them on. Flat sanding the flat side of the spacer should allow you to make it fit well if it's not too far out of spec, shimming if it's too short/loose.
Tim