Complex sentence: Leyland engine, mounted beneath the chassis and driving both axles on the rear bogie through a torque converter but problems were encounted with the Leyland engines and, in the mid-1960's, it was decided to re-engine 12 cars with 260 h.p.
Split into simpler sentences: Leyland engine, mounted beneath the chassis and driving both axles on the rear bogie through a torque converter. However problems were encounted with these engines and, in the mid-1960's, it was decided to re-engine 12 cars with 260 h.p.