Classical guitars nowadays almost always follow the traditional Spanish design with flat soundboard etc .
Years ago when I was in college there was a girl there who was a very gifted classical guitar player (and folksinger) who had a very old guitar which was Cello built .
It’s the only one that I have ever seen ( though some of the 1950’s RockaBilly bands seemed to have used cruder versions with steel strings ).
Anyway – this Cello built classical guitar had the purest tone imaginable .
Never seen another one since – anyone wanted a challenge – try making a modern one .
MikeW