I believe the SL30 contains the internal software (all commands passed thru RS232 lines) necessary to completely control it remotely. But I don’t know of any current efis or other box that has the corresponding software.
For remote Nav, I assume you are NOT talking about a GPS but rather a VOR/LOC/ILS stuff?
I would use a GNC255; and you get a second Comm for free. I have one, great little package, but not flying yet. It picks up the localizer in my hangar!!!
MGL makes what you are looking for. Here it is. https://www.michiganavionics.com/product/n16-vhf-nav-radio/