I think it's possible to do (actually someone already did one in a 1590B a few years ago) but it would require all surface mount parts to fit in a 1590B. Probably two boards, main board having parts on both sides. Anyway, not something I see taking on as there just isn't enough demand to warrant the tremendous time it would take to make such a thing a reality.
But, I do have a 125B version that runs on 18v (still positive ground). That's something I still plan on seeing through in the near future. It's in the Project Development area, called the Tourbus.