Hallo Rufus,
to rebuild the soundbox will not give you back the harp at all.
Rebuild the harp shell will need a lot of prework and at last you need very much experience in building a round shell.
Ifen if you could manage this …the most hardest thing is still to do….this is called pedal box and the sizes you need to get all in function.
I do not believe that someone could guide you thru this process at a forum.
….this work is all so much specialised…it would fill abaout 4 years of lifetime.
Best Regards