Here is a more modern engine performance graph which is unfortunately metric, from page 559 of the Fourth Ed of the Bosch Automotive Handbook.

The ovals are now total thermal efficiency fractions. 0.34 would be 34% efficiency

Torque is in Newton Meters

Instead of RPM
the nutty Bosch-co-vites
use the odd number
"Radians per Second".
There are 6.28 Radians in each shaft rotation
and 60 seconds in a minute, so the
400 R/sec figure on the bottom middle of the graph
is the same as
3,821 RPM

Do you think that an "overdrive" transmission is one
where the driveshaft turns faster than the engine RPM?

Well the Bosch-co-vite engineers define a 'overdrive' ratio
as one where the combination of engine and transmission gears can or can not
bring the vehicle up to its theoretical top speed,
so if you think your
2.76 diff gear 727 acts in all practical terms like a
3.92 diff gear 518 trans then you are in their camp.

The lines on the graph running bottom left to upper right
with numbers at their top like
0.71, 0.85, 1.0, 1.12
are 'overdrive' ratios.