Interesting thread indeed.
Unfortunately I can not spread much knowledge here,
what I noticed is just that the belly shapes WITHIN the
Gon Bops series have varied over time too.
My two 12.25" tumbadoras, one late 1970s (left), the other one 3000Series
from the mid-80s (right) display slightly different shapes, the latter one with a
fatter belly:
And the Valje shape is also very nice, the 11.5" has got an even
bigger belly than the 12.25" GB
Vergara, Requena and also Timba/Ismael,
wow, those names are awe-inspiring indeed. But the Valje makers
followed the Cuban legacy too if I remember correctly.
As I said, this is only a side remark,
I am hoping for more insight into the history of the conga shapes
of those legendary makers from the experts here...