Steering Coupler ?

That's a universal flex coupler of some sort. No idea if you can use that for a conversion on your car. You shouldn't need one of those unless you need to offset the column to get around something in the way. The stock parts should work fine in most applications. Your '64 vintage couple is slightly different from the later couples so I don't think the common rebuild kits are going to work for you. All the internal parts are different than the ones in the later couplers. Your '64 coupler has flat sides. The '65 and newer couplers have bulged sides. The bail and seal are shaped accordingly so swapping them might not cover the opening completely. The internal shoes and spring are different too but you might be able to use them as one side has the same measurement. I've made a seal for the early couplers out of an inner tube before when I couldn't find one but even if your reuse yours, if you use some spray grease under the seal every once in a while, the joint should hold up ok. When you convert to power, you'll need to change the center shaft again because the manual shaft is too long. At that point, you may find that cutting and adapting one of those U-joint couplers might be the ticket. Either that or getting the correct P/S center shaft w/coupler.