I doubt that the scale alone is the crucial factor. Ramirez 1a and 2a guitars from the 60s, 70s and early 80s have a wide neck, a 54mm nut, wide string spacing of at least 45mm, a fretboard that is slanted down on the bass side, and high action. Often the action cannot be lowered much below 5.5mm on the 6th string at the 12th fret. Have these same specs with a 650 scale guitar and it will probably feel almost identical. I've seen luthiers lower the action by modifying the bridge and saddle and by replacing the fretboard. Some also use a nut with a bit more narrow string spacing. One could make the neck thinner as well. When one thinks of how 17th- and 18th-century violins, violas and cellos have been modified to suit modern players, this is not so far-fetched. But as long as top dollar is payed for instruments in original condition, the only instruments that will be modified this drastically are 'beaters.' Which may be the best sounding and playing Ramirez 664mm guitars.
1966 Anselmo Solar Gonzalez (SP/Mahogany)
1970 Jose Ramirez 1a (CD/BR)
1972 Aria AC 40 (Masuro Matano, CD/IR)
1979 R. E. Bruné 13-course Baroque lute
1980 R. E. Bruné 8-course Renaissance lute
1990 Kazuo Yairi T-10 (SP/R)