Early balancer on 360?

If it's a street engine, just get a used 360 Magnum balancer from most any that had a two piece setup, then slot the one odd hole in your v-belt pulley to fit. If it's going to see track use or if the budget allows, get the Professional Products 90012 balancer. It can be run on your Magnum by installing the correct offset weight on the back of the balancer. Weights come with it.
I think the one piece Magnum setup started some time in 1999 model year. I have two 1999 Ram trucks, one with two piece setup, and one with the newer one piece setup.