Since your power center doesn't include space for the converter, there isn't a "hole" for a retrofit style converter to fit into. You'll want a stand-alone model to put outside the power center, not one made to go inside it.
The Progressive Industries 9500 series is great, I also wouldn't go with a WFCO.
If the area where the existing converter wires go to isn't convenient, another option is to ignore the taped off wires (take them out) and mount the converter closer to the batteries, connecting it directly to the battery terminals.