It's good to hear back from you. Nothing like setting a goal to get that training going.
I think what you should be doing depends on how you intend to go after this race. Is it just a stepping stone to “bigger and better” or is it really what you're shooting for? If it's a stepping stone, just worry about going longer. If it's the whole thing, then I'd try to do a little of both. Honestly, I hope it's the former because there's so much more you could accomplish if you're willing to step up your volume for a while before adding in the speedwork.