Well no, most times, the shims need to be thicker on one side to allow relocation of the rocker shaft in order to get the correct rocker sweep on the valve tip correcting for the poor Chrysler valve train geometry. That SHOULD BE the only reason for placing any shim under the rocker shaft.
Technically, if it isn't flat, it is no longer a shim. It is a spacer. Shim material is flat by definition. A tapered "shim" is a wedge. Exactly what you don't want exerting pressure on a rocker stand.
