The frame was designed to space the trucks at 36'-8", which is correct for a Phase 3 GE Bxx-7 locomotive. This frame is designed for Athearn trucks and the motor saddle (designed for the Kato HM-5 motor with flywheels) is situated to allow for the use of Athearn dog bone drive shafts. The frame is also designed to accept an Atlas B23-7/30-7 fuel tank, but I couldn't find any available so I designed a compatible tank and printed it.