If you're interested: from what I learned, the rear license plate on the longbed was lit two or three ways by the factory:
From the beginnings in the early 1960s, the right rear combination-taillamp had a cutout in the housing under the running/parking lamp bulb, covered by a gasket and clear plastic molded cover that allowed the same bulb to shine downwards on a license plate. This started with the two-bulbed housings on the 45s and the Stouts: (red/red),(red/amber), or (red/white).
In 1968 or so, when they first came out with the narrow three-bulbed tail lamps (red/amber/white) the idea was continued. During all this time the left side housings had no cutouts. The housing cutouts stopped with the introduction of the commonly-seen standard wider three-bulbed units in September 1973.
From Sept 1973 till the end of production in 1986 they used the bent metal plate(81484-90300) mounted to the frame up under the bed to hold two of their standard license lamps as on the FJ40s.
Brackets for the license plates themselves, mounted to the frames, started at least as early as March 1969 (75121-35010) and continued until Sept 1973. A slightly different version of this bracket (75121-60010) ran until the end of production in 1986. A listing (without a sketch) for a license plate bracket (75121-60030) is indicated for October 1982-October 1984 for LHD pickups that came with a "step-bumper," which is likely the rarely-seen diamond-plate topped chromed step-bumperettes (52150/60-90800), mounted on alternate sides of the rear frame crossmember.
While I have the bumperettes, I do not have the special license plate bracket that goes between them, or know how it was lighted. It may very well have been similar to the right-side mounted arrangement, as the bumperettes are quite far apart, and the standard light bracket and license plate mount will clear the frame hole for the wind-down spare tire.
The problem with all the license plate brackets, however, is that they put the license plates far down towards the ground, and have gotten beaten-up over their lives from steep departures or rock-crawling-- even with the angled "stay" support pieces which get hammered, all due to the extended bed overhang.
BTW, I have a 45 truck where someone retrofitted a hinged swinging bracket in place of its rigidly-mounted frame bracket, but it swings too easily while driving, and I don't want to attract a cop's attention. While not totally original, your USA style bumper can better protect a license plate, and often installed are two side mounted lamps in the recess.
As you know, Toyota kinda dropped the ball when it came to protecting the rear of these trucks, including the license plates.
