My understanding was that the Bronco sales really dropped off a soon as the 73 Blazer came out - due to it being significantly larger, which is what the buyers wanted (among many other reasons, of course).
BB, found your thread - just wanted to thank you for all the great pictures and notes. I'm planning a similar upgrade for my '90 K5, only I plan on using the version of the seats that have the seat belt integrated into the seat, likely from an SRX.
My K5 came with some sad Monroe Gas-Magnums. (It pitched and rolled more than a sweaty fat girl stranded on a waterbed. And groaned - did I mention it groaned?) My mechanic recommended KYB MonoMax monotubes. Very happy with the tighter ride.