I'm not sure why exactly they used them on these engines, whether it was to expedite assembly, or to provide a smooth transition from one piece to the next. But the engine will run with out them, much like nearly every other engine on earth. Rendering them technically UN-necessary, however given the price of FREE, and knowing for absolutely sure the ports are lined up perfectly for all practical purposes. I see no reason NOT to use them. I do know I wouldn't assemble an engine without them. Unless of course I was marooned on a deserted island and that was my only way home.
