Two outstanding builders that have stellar reputations, great personalities and are knowledgable as heck: Jim Dowdy (North Carolina) and Jeffrey Jackson (Tennessee). Both have sites. Jeffrey has an excellent blog and go to You Tube to see (hear) Dowdy's GM70.
You can also go to the Oswald Mill site and then proceed to the Tastings at the old mill in Pennsylvania. There you can read up on both builders and see some of their creations (including GM70 amps).