Sasurai Emanon is structured around episodes, so it's doesn't fully matter which order you read in, I guess. I'm not sure what the proper order is either to be honest. I was only talking about the overarching story arcs, not the order of the chapters.
Chapter 1 of the '67 arc can be read here:
http://www.mangatown.com/manga/sasurai_emanon/c001/
Not sure what arc the one on mangago is. What's listed in mangago's database as chapter 1-8 might just be a pilot, so the publisher's could check if there was still interest in the franchise, considering the first book Omoide Emanon was a oneshot? Or it might simply be a way to ease us back into the story of Emanon. Since the rest of the volumes in Sasurai Emanon covers a different time period of the protagonist's life chrnologically. The earliest time period arc I could find is arc '67. But for some reason, this particular arc is nowhere to be found on Mangago. It just jumps straight from the "pilot" to arc '73.
They jumped over the '67 arc completely and just went straight for the '73 arc! I haven't been able to find an English translation of it yet either nor find it on Amazon :((