Congrats on your find! I believe MN Schwinn is right, a 57/58. I have three and they are all 59/60. Never seen one with that early decal scheme sell in the states. Please post a pic of the whole bike. Looks very complete and original to me. I have done quite a bit of research and will be glad to help if I can. The fact the fenders are there is also awesome. Those usually get broken or taken off over time. The rear derailleur should be a Benelux like the front.