64 Lemans manual to power steer conversion
 

Can a manual steering pitman arm and column shaft coupler be used on a power gearbox? Thanks for any info.

No to both, shaft size is different on both ends between manual and power. Pitman arm available at most rest stores.

No, the splined output shaft is bigger on the power steering gearbox. The coupler is also different from the steering column to the box.

Both items are available aftermarket. If you take the box off the right donor car--A body (all GM including '69-'72 GP, Cutlass, Skylark, Chevelle, etc.) the two items above will fit your '64.

The difficult parts can be the pump and pump& alternator mounting brackets, pulleys for a '64. They are unique to '64 Tempests and big Pontiacs only. The other choice is to get all the brackets, pulleys, including alternator bracket, etc. off another year Pontiac---'65, '66, '67, and later will work if you get all the engine-related stuff. All Pontiac engines have the same bolt patterns for the brackets, but the pulleys & brackets have varied offsets so belt lineup can be an issue if you don't get all the parts.

I put a '65 LeMans power steering system on my '64 GTO when it was only a year old. Back in the day we didn't care if things like this were "correct."