Which locking hubs to use?

[MNK10]

Hello! I recently purchased a 1965 K10 with the step-side long box. I am having trouble with the locking hubs. The passenger side will disengage just fine, but the drivers side will not...They look to be original and I'm not sure if the springs inside are weak or what but it seems like it will not allow the splines to completely disengage.

I'd be fine keeping them if anyone has suggestions on how to make them work as I won't be using 4x4 often. But if I was to replace them does anyone know if the Mile Marker 104's would work on a '65? When I try to cross reference their products it seems like most of their stuff starts in '67.

Any info would be helpful, this truck is mashup of a few different years so I am playing catchup!

Thanks