This isn't going to help much, but I've got '96 heads on my truck now, (350) with 1987 accessories bolted up. I also had 1974 brackets bolted up to the Vortecs, they worked fine.
The 4.3 is essentially a 350 minus two cylinders, there should be no major differences between them in accessory mounting. Perhaps on the new new 4.3's, but I suspect since their inception to at least '96, and probably later, the face of the 4.3 is the same as any other Gen1 (think thats right) small block.
FWIW, I used the drivers side PS pump bracket spacer from a 4.3 truck to bolt my PS pump up in my truck with headers. Perfect fit! /forums/images/graemlins/smile.gif
I'm only posting because no one with more 4.3 experience has spoken up, hopefully you'll get a more definitive answer.