Lots of interesting questions but very few answers I have x)
All screenshots from this post come from my February 79 Master Catalog which covers all Land Cruiser from 03/69 to 02/79.
I have no particular knowledge on the -B suffix for the pickup and when short bed pickups were a thing, Toyota was still long away from coming to Europe so over here the long bed pickups are the only one we know.
But looking at this:
The suffix letters are not clearly explained anywhere, they are just letters that designate a specific version. Pickup had the -B up to 7501, from 7501 they only had suffix letters to designate gearbox type and and market specific version.
But now if you look at the FJ55s in the right... up to 7501 VKC (ambulance doors) FJ55 had a B while the VTG (tailgate) FJ55 had nothing. From 7501 the -B became -C for some reason...
Looking at the 40s table the VKC ones also got the -C (from 7204 when VKC started on 40) while VLS had nothing.
All of that to say that -C replaced -B and clearly it designates the 2 different types of back on a Van or Station Wagon. So I think we can extrapolate that on a pickup it was also used to differentiate the 2 kinds of back, so nothing=short bed, and -B=long bed. And from 7501 they considered the short bed was long gone and forgotten and removed the suffix.... Just a supposition.
For the production number there is a revision table that gives a revision code to every frame number range to know if your vehicle is concerned by a change.
Revision code 875 is the last with chassis numbers, so 02/1979 and we have HJ45-027056, and FJ45-199464.
So I think this give you numbers at this date.
There is no table of date for each revision code but it should be possible to search for each revision code in the master catalog to match them to a date to deduct production per year... But who got time for this? x)