I went to my university and found a great book: "Feodal Britanny from the XIth to the XIIIth century". Here are the modifications concerning county of Léon:
Unfortunetly, there isn't a lot of pieces of information

. Nevertheless, I found that the first known viscount was Guyomarch. He died in 1055.
Secondly, after Guyomarch the first, there aren't any historical sources until Guyomarch II who dies in 1103.
According to several genealogical websites, Guyomarch was born in the 1030's.
Consequently, all characters in county of Léon should be removed except Guyomarch II, born in 1035. I haven't any idea of his attributes Jordarkelf, just make him a tough soldier. BTW, I think we can give him 50 prestige points at the beginning since the viscounty was the less prestigious title in Britanny.