It's been a while since I've done this so bear with me if I lead you astray at all - but I saw there are no posts yet so I'll give it a shot. Yes the knob will come off without breaking it, but it'll be a little bit of a battle. First pry the shiny plastic cover around the o/d switch out, then lift out & unplug the o/d switch. Either give a solid yank on it or place an open-end wrench under the handle & tap with a hammer. Be forewarned if your nylon shifter bushings are worn or cracked this will finish them off, but you wanted an excuse to replace them & make that shifter tight as new again, right? The reverse lockout ring is, as I recall, held onto the rod running down through the shift lever with a small (#1 phillips head) screw, into a recess in the top face of the ring below the shift knob. If that's missing you've found the problem. Or the lockout ring may have cracked around the screw hole. The pull rod may have broken off inside the shift lever, and in that case I suggest getting a good used shifter assembly, you'll need some bits & pieces from it or ideally just put the whole thing in your car. Should only be a few dollars at the pick-n-pull but the 4mm grub screw is only accessible from under the car so find one that's at least got its wheels on it so you can slide under a bit...
In a pinch you can just lift up the shifter boot & you'll see the lockout & how it works - just lift up the lockout so it clears the interlock plate. Or loosen the 2 8mm bolts & slide the plate all the way left, that should give you enough slack to shift into reverse without a lockout. Shifting from second to first is to be done with extreme care if you do this, of course. Good luck!
-Chris