One sure way is to contact the builder. William Webster, Warren, MI, (313) 570-8385. Or that is the number I could find. Have the serial number handy. Or Michigan Harp Center. Someone here might have a string chart also.
Last, if you haven’t done it before, for heaven’s sake have a technician do it or teach you. There will be a lot of tuning required to stretch the strings in.
Frankly, if they are not broken, and you won’t be playing, I wouldn’t string until a month or two before you start. Just keep it in reasonable time.