NP540OD will fit where the NP540 will, but they are a bit scarce, and parts are scarcer. There was a yard in SO Cal that had a couple of each, but I lost the link. You might need to get the input shaft from the Dodge version of an NP540 to put in the NP540OD to make it work, as I understand the case, input shaft and bearing retainer were the main differences between the various aplications of the
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Dodge Sweptline Truck General Discussion