I realize you have an 1960's model that didn't come with a factory radio, but you might want to consider how it was done on later models.
On the 1983 LHD longbed there is a factory welded nut to receive the lower factory antenna mount inside the truck on the Left A pillar between the kick vent opening and the lower left door hinge With it there is a corresponding hole drilled to receive the antenna lead, and another welded nut further up the inside A pillar on the cowl for the upper mount.
On the 1982 LHD longbed, and on the 1979 LHD FJ43, the same factory holes and nuts appear on the Right side A pillar to accept a factory antenna.
On the 1980 LHD longbed there are no factory mounts, and the local dealership typically mounted the antenna on the Right side in the same A pillar location, or forward of that between the kick vent opening and the louvered side cowl.
The above are LHD trucks and show variation between Left and Right; and perhaps things got reversed should you have a RHD version. Maybe there are some photos out there showing these or other variations over the years; maybe some factory sales brochures for various export markets that offered the optional radios.
Some drivers voice concern that various antenna locations can be distracting in their line of sight, some argue for being able to wind down the window and fiddle with the antenna whilst driving, and certainly mounting the early-style A pillar mirrors might interfere with the antenna when also mounted on the A pillar--- so I guess the choice to be "correct" is wide open to you.
Another related issue is where the CB whip antennae got mounted during the 1960s to 1980s--often behind the driver's line of sight on the curve behind the Left seat, similar to the location of the filler neck on the right side. But here again, there doesn't appear to be a "correct" location.