Pep was a big comic magazine around 1970. They did publish Prince Valiant in 1970 and 1971.
They seperated the plates in 6 full stories with the following titles (and behind the title is the Pep Issue number).
There are two plates printed in each Pep Issue
1 De gezant van de koning, Pep number 7031-7041
2 De opstand van Cidwic, Pep 7042-7049
3 Valstrik voor Valiant, Pep 7050-7102
4 Arn en de Saksers, Pep 7103-7107
5 Strijd om Thule, Pep 7108-7112
6 Arn in Niagara, Pep 7113-7122
Value around 10 Euro's for the early numbers.