Opinions on tattoo coverup?

I have a 17 year old tattoo on my shoulder that I'd like to modify/coverup. Here is the existing tat: http://i.imgur.com/tZPu5.jpg. I'd like to turn it into a Viking (skull face with viking helmet, maybe broadsword, etc), and add some runes and some banding designs around it...not completely sure, I'd like to begin toward a nordic themed half-sleeve. Just wanted some opinions on feasibility before I seek out a local tattoo artist. Thanks.