OK, while seting the valves on my friends 66 Valiant I noticed that several of the rocker shaft assemblies had extreme lateral movement. Is there a shim kit for this or is this normal? I can always swap out the ones that are loose with tighter ones from his old engine. What would the rocker shaft bolts be torqued to? Thanks.

A small bit of lateral movement is normal. "Extreme" is not. Shims aren't necessary, but it is necessary to make sure all the correct spacers are in all the correct places. It sounds as if one or more spacers might be absent. There's a very good diagram in any '60-'80 factory service manual for a slant-6 car that shows the order of the rocker shaft components.