Here's what the pickups look like. To me, they look much closer to real '60s Thunderbird pickups than the ones that came later in the reissues.
I'm no expert, but don't the originals have blade magnets? Yours looks like it has a magnet on the bottom plate instead, like the 80s and later pickups.
Where do you see a bottom plate magnet, Dave? Looks to me like a 60's bird pup with different sized bobbins.
These pickups have the blade magnets only. There's nothing on the bottom plate except some remnants of adhesive. It's not really even a baseplate, just sort of a very thin tin cover.
Just for reference, how wide are those blade magnets? I've been looking for T-bird bobbins and magnets for some time now..
It wouldn't surprise me if they were standard humbucker size magnets.
All I can say is that all early TB Plus innards looked like that and that there was no dif between Bass IV/V and '87 onwards TBird mounted ones. Changes came later.