The engines in the SD40Es are 16-645E3Cs. The SD50s had 16-645F not F3 engines. The engine block for all 16-645 engines are the same wether it is a 645E, 645E3, 645E3C or 645F. The difference is fuel system config and turbo or lack of a turbo. These differences account for the difference of horsepower of the engines. 645E is 2000HP non-turbo, 645E3 is 3000HP turbocharged, 645E3C is 3000HP turbocharged micro-processor equipped, and 645F is 3500HP turbocharged. NS rebuilt the 16-645F engines to 16-645E3C by changing the turbos and other thing like adding the micro-processor. With these changes came the horsepower derate from 3500HP to 3000HP. All that description was said to say this, the 16-645E3C is not the same as the 16-645F. They have to same block, heads, ect., but that is where the similarity ends.Actually the NS reused the 16-645F blocks(crankcases) from the the 50 series units and remanufactured them to E3 specs for testing on a couple of these SD40E units, but not all of them due to the unmatched reliability of the E3 block. The F3 in the SD50s had an abundance of oil feed problems and the fact the oil lube lines, feed lines, and pump were famous for failing and causing the crankcase to starve for oil which creates internal friction and valvetrain misfire and slippage and blows the dam crankcase. This is why NS is sticking to the E3s for the 40Es. I dont care if I win, but honestly both engines should be deemed as an appropiate answer. The block is the base for the engine and when a F3 block is used and remanufactured to the E3, you pretty much two engines in one due to the mixed parts.
Paul