Exciting news! I was doing my usual weekday time-waster: googling around for "motorsailer", "Ta Chiao" (the builder) or "Perkins" (the engines), etc. and stumbled across a forum entry at yachtforums.com by one Brian Eiland, a boat designer here in the DC area. He had apparently seen Blanca (previously "Gypsy") on the hard at Tall Timbers, and wondered who designed her.
The thread in the forum had a posting of a 1970 magazine-ad for a boat design, the Rhodes motorsailer "Discoverer." The artist's concept picture was Ballena Blanca!! I was amazed. Another poster, Ben Stavis, linked to his own website about the designer, Philip L. Rhodes. Here's his page. Philip Rhodes was a boat designer of some note who designed yachts from 1920 through 1970. My boat, his design #816, was one of his last designs in 1969. He died in 1974, and his plans and design materials were donated to the Mystic Seaport Museum. I've sent them an email asking about the extent of their holdings about this design, but they haven't answered yet.
This is so cool!! I had never imagined I'd find out this kind of information about Blanca. Thanks to everyone who helped find this out!