To date, I have never encountered an AHM HO-scale Century 420. The three road names and stock numbers presented are from a mid-1970s AHM price listing with no pictures.

My guess is this would have possibly been the Lima Century 420 model. Lima's Century 420 did find itself available in the 1970s in the U.S., but it was sold by Model Power/PMI and not AHM. For a time in the 1970s Model Power had a secondary line under the PMI, Precision Models Inc., name and this line included what I believe is the first American release of this Italian-made HO Century 420 offering. The February 1976 issue of Railroad Model Craftsman includes a product review of this model. The PMI roster included the trio of road names promised from AHM (Penn Central, Santa Fe, and Union Pacific) and added a Canadian Pacific release.

By AHM's 1977 catalogs and price listings, there is no mention of this model. As a Model Power/PMI release, the Lima Century 420 was available decorated for Santa Fe, Union Pacific, Penn Central, Canadian Pacific, Spirit of '76, and Chessie.

Lima also sold the model under its own name and it was available here in the U.S. from them. Among that release is an interesting Southern Pacific Daylight experimental scheme.

Similar to its FP45 sold by AHM for a short time, this Century 420 presented swinging pilots attached to the trucks in a Lionel-like design. Lima also produced a high-end Century 420 model that included finer detail and omitted the pilots mounted to the trucks. MRC (Model Rectifier Corp.) originally marketed this enhanced HO Century 420 in the U.S.