Will Vincent or Tubes for hifi both rebuild but they basically use the case and transformer. Those are 1700-2000. They sell kits as well.
We used to have Magnapans. We used Ampzilla and Quattre. Both blew up. There were some reliability improvements that can be made. Bonjoirno and Leach put solid state on the right path. Much more pleasant sounding than many of the day.