According to EPC it depends where your engine was made - you can find out by the first two digits of the engine number:
TA = Tonewanda, New York
11 = Kaiserslautern, Germany
2. Screw,M8 X 40,Camshaft Bearing Cover to Cylinder Head (KAISERSLAUTERN) - 11518051 (x2)
2. Screw,M8 X 40,Camshaft Bearing Cover to Cylinder Head (TONEWANDA) - 11516339 (x2)
3. Screw,M6 X 40,Camshaft Bearing Cover to Cylinder Head (TONEWANDA) - 11516427 (x20)
3. Screw,M6 X 40,Camshaft Bearing Cover to Cylinder Head (KAISERSLAUTERN) - 11518066 (x20)
Probably best check with local Vx parts department.