Victor Penner said "If the Monark is a Masi I believe it would be from before he was a Pro riding for Ferretti and Magniflex. A "Monark" for a Swedish amateur makes sense, National Team, National Bike."
This seems correct. Bob Hovey dated the frame as '69 or '70 in responding to Charles Andrew's comment that it was probably a Masi Special. A biography of Pettersson (link below) says "...In the late 60's Gosta Pettersson was the dominating rider on the amateur level in Europe. ..." and says Petterson turned pro in 1970.
http://zkahlina.ca/
Peter Brueggeman
La Jolla California USA
4peebee(at)peterbrueggeman.com