I'm looking for some dual sport tires for my '91 K75 and have spent hours on this but I'm not having any luck. So do I just get a set of those and add tubes? Are there just really no tubeless options?
You're having having luck, didymus, just not
good luck. You just get a set of those—if there is no fork or swing arm interference using them—and add tubes.
The classic K is not a dual sport; it's a road bike and an old model at that. The knobby market ignores their owners' perceived needs. You'll need to make compromises. You've already discovered you'll need to accept a different size/profile. Some knobbies for true dual sport wheel sizes are tubeless.
True knobbies in sizes that fit
your rims will need inner tubes
The Shinkos you're indicating for installation on the front and rear of your bike are
both rear tires. A rear tire on the front will change handling characteristic on a paved road at speed. They'll also wear faster. If you're skilled, you can deal with it as many before you have.
The Kenda K761—as posted in this thread—is a tubeless quasi-knobby with mixed reviews that will fit your bike but it's unlikely to perform as well as a true knobby in the back country. It has discouraging reviews about performance on wet paved roads, too.
Threads about knobbies have been posted here almost to
ad nauseum levels. You should have much less trouble finding them than finding knobbies.
