Steering box?

[smallblockwagon]

I am looking to change my steering box from this old worn out
c-clip style to a 4 bolt box but the pitman arm shaft seems to be
larger on the 4 bolt box aside from the fact it is non serviceable item
how do I identify the arm that I need?

 

[patmckinneyracing]

What is the four bolt box from? I swapped mine out from the c clip to a four bolt from a monte carlo ss. So i had to get a pitman arm from a monte carlo because it was a hundreth larger than my malibu's pitman arm.