Wow! Welcome to the forum Colin and thank you for sharing these with us. Pretty amazing to see the original concept models for Star Wars '77 and having the chance to discuss them with their very creator.
Regarding the original Falcon, am I correct in assuming that it was still used in a re-purposed and heavily modified state as the Tantive IV Rebel Blockade Runner (or for inspiration at the very least)? They both have a very similar basic shape and overall design is all, with the exception of the front bridge area and the rear engine area having tripled in size:
It did indeed become the Blockade Runner. Somewhere I’ve seen an old BTS photo where the Tantive miniature was still being finished, sporting the Falcon style cockpit and deflector dish.
You can’t really see the cockpit from this angle, but you can see the Falcon’s dish.