You can also double-ink the press if the quantity you’re printing isn’t too high.
Good to note the addition of silver; I’ve letterpress printed PMS 877 Silver by first printing in opaque white, then doing a second pass with the silver ink. The opaque white seals the sheet and acts as a good primer for the silver to really stand out. Note that this is on a Windmill, where registration is precise; I’m not sure I would recommend this route for most other presses where registration is more difficult.
Lars.