I've mounted this style carrier on my 1999 Lexus LX470 using the following:
Lower retainer, sub-assy, spare tire carrier: 51907-60070 (bolts in with minor drilling required)
Bolts for above: 90119-08093
The "right" way to do it would be to install one of these as well 61033-60090 but instead, I cut off the upper retainer and welded it directly to the body back inside there (not pretty but it has held a 37x12.50r17 MT and a pretty heavy wheel - 130lbs I think)
The U.S. spec hatch needs support behind the the bumper/stopper 51905-60020 so I cut/bent some pieces of 3/16" and braced it behind the door lock mechanism (it's close to being in the way but not quite)
I made similar modifications to the tailgate and added more 3/16" steel to support the striker plate. It holds to majority of the weight of the carrier compared to the hatch stopper/bumper. I would strongly suggest someone add additional bracing to the tailgate as it feels the most flimsy out of all.
I've opened and closed the same assembly on overseas 100s which came equipped from the factory with this mount and they feel a solid 40-50% stiffer than my "retrofit."
I give it 1-2 years before something gives way.
The tailgate and hatch from overseas models are both different but will obviously bolt onto a 100 body as long as they're the hatch style (not barn doors).
One other major modification I made was actually to the support arm itself. I cut off the tire carrier and moved it up about 10-12" to gain as much clearance as possible. Without doing this you actually lose departure angle rather dramatically-
Unfortunately this meant that the cable-release lever was un-reachable so I welded another vertical brace in the carrier arm and welded the cable-release to that.
If someone was really being fancy with it they could add a door ajar sensor on the hatch circuit. The striker plate and assy have spots for them.
Photos to follow (five included here)
By no means am I trying to scare anyone from attempting this. I don't have any formal training in body work, vehicle modification, or maintenance for that matter. I'm just a "hobbyist" who happens to love tearing up his truck. It's doable but be advised that it will take a lot of work (or money).
Above: OE tire carrier
Above: Patch's modified OE tire carrier on U.S. spec '99 LX470
Two JDM 100s with OE tire carriers and one 1999 Lexus LX470 (U.S. spec)