I have more to post on this... but I didn't want to do it all in one message: figured I'd see if there was any interest.
I agree that I like Adam's renderings of his designs better. They feel sleeker than McQuarrie's take. I would've loved to get my hands on the study models...where they sold at the auctions?
I edited the Planet of Titans
entry on Memory Alpha to make it more accurate, and also corrected some of the captions which attributes the Titans designs to Phase II (and added an entry for Study Models, since they erroneously referred to the study models as Studio Models), and I revised their entry on McQuarrie
to correct Titans errors there, and to add mention of his work on Star Trek VI. Whew!
There's an entry on the project in "The Greatest Sci-Fi Movies Never Made".
As to Mifune...I love the man. I love him in High and Low
in particular, amongst many great performances. I was thrilled when I picked up a capsule toy in Japan and opened it to find it was Mifune as his nameless Samurai from Yojimbo...in black and white! Yay!