Well, you have a few options, but there are no 17" tires that do everything right. The Avon Distanzias come in the right sizes for the Baggy and work remarkably well off road, especially if you lower the tire pressure before you tackle anything too slippery. The tread blocks are a bit large, though, so when it comes to really loose stuff, they can slip quite a bit if you push too hard. The Pirelli MT60-Rs do really well too as long as you remember that you're on a heavy bike with limited traction, but they have a tendency to wear pretty quickly. The best bet for taking heavy dual-sports off-road is the Continental TKC80, but they don't make a 120-17 front. They do, however, make a 120/90-17 rear that I GUESS could be used as a front. I don't know the particulars, but you generally hear that a tire meant for the rear shouldn't be put on the front. I do recall a lot of customs using huge front rims running rears on the front, and the Royal Enfield Bullet runs an Avon front tire on the rear. Consult someone who knows better, in other words. If that whole deal doesn't work out, you can at least use the 150/70-17 rear and the front avon or pirelli.
The Continentals can be seen at Continental's site here:
http://www.conti-online.com/generator/w ... 80_en.html