Hello @Polymaker
i enjoyed reading your thread. Maybe you have completed your project now? I can tell you that the Höpf Saturn 67 bass I have DOES have a solid carved top. I can try and post a picture taken from under the control panel. If you need any measurements I can help. As far as I am aware the six and four strings have the same body. I also have a Höpf Jupiter neck six string neck (for another project) I can measure. This would fit the Saturn I am sure.
let me know how you progressed!
And does anyone out there have a finger rest for a Hagström Coronado bass please?
matt