Thanks to everyone for their comments and suggestions.
I wasn't aware of the Kohler models with the side clips that fit on the flange. But I've not found a model that is any better than what I already have installed.
Not sure I can drill just 1/2" into the tile. From the template, it looks like the holes go right on the edge of a grout line. I'm not sure I can get a tight fit for an anchor.
For the Toto installs that weren't anchored into the floor, could you tell if they used any type of adhesive or sealant to keep the adapter in place or was it just loose on the floor.
Right now I'm thinking of two options.
One is to get a 1/4" plate, tap and put some studs in to bolt the adapter to, put an angle across the back of the plate and anchor it into the wall behind the toilet. If I do this, should I add a 1/4" flange spacer too.
Or I could get a 1/4" plate made that I can bolt the adapter to and can be also be bolted to the closet flange to keep in in place. I'm assuming I have enough space under the back of the toilet to add the 1/4" plate.
Anyone have any additional thoughts?