can any one tell me if a Conti Motion Sport Touring size 150-70-17 would be ok on the front of the valk
"Darkside front" or "double darkside," means using a motorcycle rear tire (generally mounted in reverse rotation) on the front of the motorcycle. By starting with 11/32" tread instead of the normal 6/32" as typical on "front" tires, you get much more mileage out of it.
As for your question: The 150/70/17 is about 1 3/8" shorter than the original tire, causing a BIG speedometer error. I'd suggest a 130/90/17 to maintain the height of the original tire.
I personally have a 150/70 on my Valk and register a 10 mph error as compared to the GPS. The error was only 3 mph before I went to this size tire.
BTW, My Kenda tire with 13,000 miles looks like it has the same amount of rubber on it as my friend's "normal" front Avon tire he installed last week.