Generally speaking, M40 4-spd sedans and coupes got 4.10 rear ends. Wagons got the 4.56. And I think coupe/sedans that came from the factory equipped with the M41 overdrive trans got the 4.56 rear end as well.

Advantage of the 4.56 rear end: Acceleration. More torque multiplication, pulls harder in lower gears, but you have to shift sooner.
Disadvantage of the 4.56 rear end: RPM at speed on the highway goes up (offset by M41 OD trans). MPG goes down slightly. Makes keeping up with modern traffic speeds feel somewhat abusive with the motor spinning that fast.

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'63 PV544 rat rod, '93 Classic #1141 245 +t