The Allen screw bolts should be either 6 mm thread maybe 5 mm, I forget which. I would either find a used set of the runner to head adapters or take yours off the car. If just the fasteners are damaged replace them. If the threads are damaged I would either clean the threads up with a tap or helicoil any trouble spots. The problem with the Allen bolts is tightening them or loosening. I have a long ball end spocket the helps in this process. A standard Allen key socket or wrench will not allow any misalignment without the possibility of stripping the fastener. Any air leaks in this spot will effect idle and performance.