Methinks you would need the /6-727 adapter used in some trucks, taxis and fleet vehicles.
An A500 or 518 should then bolt up. Depending on the year it is sourced from, you may need the crank hub adapter bored out to accommodate the later torque convertor. Also be aware that the later OD transmissions require some reasonably substantial trans crossmember modifications and fabrication, especially in early A bodies.
Three other alternatives come to mind:
1.) Drop (numerically) your rear end gear ratio. IE, if you have 3.55:1 rear gears, swap them out to 3.23s or 2.91s.
2.) Taller rear tires.
3.) Install a non-overdrive transmission with a lock-up convertor, such as the 32RH. Not as effective as an overdrive, but it does drop your cruise by a couple hundred RPM. It would still require sourcing the 727 adapter, but does not require cutting and rebuilding your crossmember. The only mods would be relocating the trans mount a little further back (equal to the thickness of the adapter) and a bit of relief grinding of the reinforcement ribs on the tailshaft of the 32RH.
Also note that any of these trans swaps are going to require all different shift linkages, driveshaft and speedo cables/hookups; since none of your '65 cable shift linkages or ball & trunnion driveshaft will be compatible.
Honestly, 1 & 2, or a combination of both, should get you where you want to be with the least amount of hassles.
