I haven't installed mine yet. But the valve springs are the same as what comes in the P5160074 kit (for a bunch more) and the text there says no shims required. Works with the factory seats, retainers and locks.
P5160074 - Genuine Mopar Performance Valve Springs
Is there a seat under the spring to protect the aluminum head and that is being confused as a shim? I went and looked at my heads (2017 5.7 Ram) and there is definitely something between the head and the springs.
