Yes, this Adafruit board is stackable. With multiple boards you can have just under 1,000 servos.
There are also boards for driving many LEDs.
Read up on I2C and SPI interfaces.
edit: Plan for more servos. As soon as you start doing this, you will want to automate crossing gates or other pieces and your servo count will grow.
Also, Wow, 70 turnouts. Pics or it didn't happen!