So the 120mm bolts were not really long enough with the original Porsche flange nuts, the thread didn't fully engage. Although it was easily enough to torque them up fully, I had a nagging worry about them coming loose.
The problem is that 140mm bolts are too long (the un-threaded shank extends beyond the engine X-member) and 130mm bolts in 10.9 steel are unobtainable, in fact 8.8 bolts are almost completely unavailable too. By chance I found that BMW use M12 130mm 1.5mm thread bolts and the part number is 07119906978. They're £4.25 each from you local dealer, only 8.8 grade but I decided that was strong enough on such large bolts. They are also zinc plated and should last well.
The problem is that 140mm bolts are too long (the un-threaded shank extends beyond the engine X-member) and 130mm bolts in 10.9 steel are unobtainable, in fact 8.8 bolts are almost completely unavailable too. By chance I found that BMW use M12 130mm 1.5mm thread bolts and the part number is 07119906978. They're £4.25 each from you local dealer, only 8.8 grade but I decided that was strong enough on such large bolts. They are also zinc plated and should last well.