you have a 69 C6? I didnt read that.
DUMP ALL THE OLD FLUID OUT.
drain torque converter, drop pan, change filter, blow out cooler lines.
Replace with:
Mobil 1 ATF
Mercon-V ATF
Amsoil ATF
Quaker State Synthetic Blend 4x4 ATF
any one of those will be fine.
My dad's 89 E-150 had a C6 and Ford specified Mercon.
Type F is still used on a few modern cars, I don't know why.
If anything the friction modifier properties of Type F are slightly different from that of Mercon or Mercon-V, but the brands I listed are synthetic or synthetic blends w/ much better properties than the ancient Type F. All Ford PS units use Mercon now (at least in their real vehicle lineup: V8 trucks, vans, and cars) whereas in the early 80s late 70s Ford specified Type F.