The park finish could be original for a late war build Eddystone. In fact having a mixture of finishes would also be correct as long as they are all the parts are marked E. Only Eddystone adopted the park finish during original manufacture but assembled them with already made parts most of which were still blued. This can be referenced in the Remington society article on the P14-M1917. It boasts how they were able to reduce manpower by going to the park system over the rust bluing.