O.d.

I've been driving a 1980 D100/150 that's had a somewhat built 69 440 transplanted in place of the factory slant 6 and bolted to the factory 833 O/D.

I've done plenty of "spirited" driving.

It's fine.

I personally would not power shift any transmission into overdrive.

When driving hard, I like to think of the shift pattern as a three speed with a better 1-2 throw.

Stay in 1:1 until you feel like relaxing, then shift to O/D and cruise.