Jim,
Two tail lamps are smart from a safety perspective regardless of when your car was likely produced. Both the right and left-hand brackets were in existence from Job #1 as the right-hand bracket was used on RHD cars. It was only the crossover wiring harness that needed to be created to permit the use of two lamps.
You are correct to use the same tail lamp housing for both sides as that is all that Ford released for the '32 models. No block-off was offered for the license plate lamp opening for the housing used on the side opposite where the license plate and its mounting bracket were attached (right side in your case).
You have any number of options, including just letting the license light on the right side shine up on to nothing. Way back when, someone (not Ford) cast the glass license plate lens in clear red and these turn up from time to time at swap meets and on eBay. I would have thought that such a lens would be an ideal candidate for reproduction, but so far I am unaware of it having been done. Another option, is to paint a an original or reproduction license lens red using the special paint I've seen on eBay (and elsewhere) used to restore faded plastic tail lamp lens. It is a translucent paint and it adheres to clean glass quite well. The only difference between doing that and finding one of those old aftermarket lenses is that the aftermarket lens lacks the stippled surface on the inside of the lens.
You may have missed it in the book (page 6-23), but Ford did release a two-bulb tail lamp housing without an opening in the license plate lens (other wise identical except for the absence of the "DUOLAMP" name), but not in North America and not for '32 models. Having encountered a couple of these lamp housings in Europe along with the clear evidence that they had been attached to '33-'34 tail lamp brackets, not '32 tail lamp brackets, I finally ran across documentation of their existence at the Benson Ford Research Center. That documentation confirmed the circumstantial evidence, namely that their use was confined to '33 models sold in Denmark and Switzerland where (evidently) local automotive lighting standards required separate bulbs for the brake lamp and for the tail lamp. (As you may know, Ford switched to a double filament single bulb for its tail lamps starting with the '33 models along with unique right and left-hand lamp housings.)
The reproduction Model A/'32 lamp housing available without a license lens opening and stamped "DUOLAMP" are is product of someone's imagination and not a replica of an original Ford part.