Personally, I think that you can tour on anything that's comfortable to you.
I rode a Kona Scrap over 400 miles, including a few 70 mile days. It's certainly not ideal, but that depends on how far you're going.
If you can ride it all day, then by all means go for it... some stuff will wear out, and you'll eventually get an idea of what you like and dont like.
I'd say that if I was "converting" a mountain bike I'd do two things right away.
1. get some smooth, tough tires.
2. replace a suspension fork with a rigid one, Surly sells some that aren't too pricey.
Then I'd either get a rack/panniers or go with a trailer. I did the trailer with the Kona for obvious lack of rack-bosses.
how far are you planning on going?