Complex sentence: The ZiS-151 engine was closely copied from the Hercules JXD used in Studebaker US6 trucks supplied under Lend-Lease, a L-head inline 6 cylinder gasoline engine developing at 2600 rpm.
Split into simpler sentences: The ZiS-151 engine was closely copied from the Hercules JXD used in Studebaker US6 trucks supplied under lend-lease. A L-head inline 6 cylinder gasoline engine developing at 2600 rpm.