Two more former Carrera Cup cars have been registered for the Michelin Porsche Open Series ahead of the third race of the season at Castle Combe on Monday (2 May).Racing newcomer Mark Stephenson from Cheshire will make his racing debut in round four at his home track of Oulton Park on 14 May in a 911GT3 Cup car entered by ABG Motorsport.Meanwhile, having campaigned a 944 Turbo over the last two seasons under the wing of Track Torque Racing, Simon Mifsud is moving up to class two of the Porsche Open with an ex-Peter Chambers 911GT3 Cup.