Was playing around online and found the following story on the famous bridge/tunnel that crosses the bay today. One of the pics is of particular interest, as the ferry pictured, bears a very strong resemblence to the Tswassen and Sidney in their original form.
The S.S. Pocahontas was built in 1941 for the Virginia Ferry Corporation. As built, she was 282 feet long, but she was later cut in half and had an additional hull section added to which lengthened her to 358 Feet. The Pocahontas was powered by two steam engines and served on the Chesapeake Bay crossing until 1964 when she was sold to Delaware for service between Cape May, N.J. and Lewis, Del. The Pocahontas carried 1,200 passengers and 120 vehicles.
The SS Pocahontas was renamed the SS Delaware when taken over by the DRBA in 1963 for the Cape May-Lewes route. I'm assuming she was replaced by the new-builds in 1972, and it looks like she was scrapped in 1977. Info about scrapping found here (see hull number 442/1074).
It's definitely the Pocahontas as the Princess Anne didn't have the downward swoop at the bow (though the photo of the bow could mislead you as the doors being open sort of gives an illusion that she had one, too).
Being that these ferries had been in service for 20 plus years before Spaulding designed the Sidney & Tsawwassen, he may have incorporated some of their lines into his new designs...we're speculating anyways, so...