Just to be clear, the LFR5C-11 are stock 09+ 5.7 plugs and are the same heat range as the stock 6.1 plugs. They are not interchangeable as the 6.1 head uses a tapered seat plug and Eagle head uses a gasket type plug.

The LZTR5A are stock heat range 6.1 plugs, and 1 heat range colder 08 and older 5.7 plugs.

If a tapered seat plug is installed in an Eagle head it's probably best to keep using a tapered seat plug from that point forward. The tapered seat plug will deform the area around the "seat" of the plug in the head and will probably make sealing a gasket type plug problematic in the future.