This is an optional Tekno RC EB48/SCT410 Hard Anodized 7075 "Bumper Mod" Chassis. The two front-most holes on the original EB48 and EB48.2 chassis were not countersunk because the original bumper covered them. However, testing has shown that you can gain ground clearance by cutting the front bumper area that goes underneath the chassis, for improved performance. So, the guys at Tekno decided to countersink the two front holes, allowing the bumper to be secured with just the M3x8mm cap head screw that mounts to the front outer hinge pin brace.
Other than the front two holes being countersunk, the chassis is identical to the original chassis.