Ball joints spinning so cannot tighten AND castle nut issue

[HeavyHauler]

Well I pressed in new lower ball joints for the lower control arms of my 1968 Chevy C10 and now I am trying to install the spindle but the lower ball joint stud keeps on spinning and will not allow me to tighten it.

and also the new castle nut that came with the ball joint is very skinny and i can spin the nut on by hand and can get it below the cotter pin hole and I havent even torqued it down yet....if I did torque it down the cotter pin would be sticking out waaaaay above the castle nut.

The old factory castle nut is about 1/4 inch thicker so I decided to use that as I figured after I get it torqued down really good then I could install the cotter pin

What do guys do in order to stop the ball joint from spinning. None of the tricks I saw online seem to work like putting pressure on the spindle area with a long bar to try to bind the stud so I can torque it down.

I got frustrated and used a impact gun on it and got it to tighten down so that the tip of the stud is even with the top of the castle nut but the stud is still spinning.