The Longships Rules From Peter Pig Are Now Available in PDF Form
They are not skirmish or big skirmish, but battle rules. The rules include some exciting and revolutionary mechanisms that work very well for the 9th Century (sorry, no Normans, too early).
PP make a full range of 9th Century Vikings and Saxons.
The printed version costs £18.00 GBP from PP, and is also stocked by Brookhurst Hobbies in California. The PDF copy is £9.00 GBP direct from PP.