This house rule replaces Russia restricted. All IC are limited to a maximum number of units produced per turn equal to the IPC production of the area they occupy. So the maximum production for the Karelia is 3 units per turn. 8 units per turn for germany, 6 for southern Europe, 8 units for UK, etc.
SBR has an additional effect for every bomber that successfully completes an SBR (i.e. not shot down by AA) place a chip under the IC bombed. The max unit production of that area is reduced by 1 unit for each chip under the IC. All chips are removed at the end of the placement phase for the owner of the IC. This SBR effect is in addition to the normal IPC bombing damage. Heavy bombers place 3 chips under an IC for each successful SBR.