PD and powermax make direct replacements for current WFCO assemblies, don't know if it will fit yours, but Randy at Best converter will let you know if you give him the WFCO model number.
If you seldom boondock, another alternative is to just replace the existing WFCO supply with another WFCO. My experience is that the WFCO's are reliable, very comparable to PD. The big downside is if you dry camp, the current 55A model is prone to not going into bulk charging mode so it takes forever to get the battery charged. But if you don't boondock, not as much an issue.
And the current WFCO is certainly much quieter than the PD replacement.