100% agree, CJ-D, however there is no automated way to check if something has been previously approved elsewhere in Europe, because there is no central database.
The CAA had its AAN database (which was pretty incomplete because a lot of US STCd items were "just fitted" in the belief that the old CAA-FAA treaty allows this) and one or two other countries have something similar.
Beyond this, to see if somebody in Europe has done a certain mod, the simplest way is to contact the U.S. manufacturer of the item and ask them if they sold any to Europe. If they respond, then ask them who they sold it to. If they reveal that.... then you can ask the European installer (an avionics shop, perhaps) who, for a fee, might be willing to send you the details of the job and their local CAA approval number or whatever.
So yes it can be done but if somebody is importing a plane onto EASA-reg, it is generally easier to avoid these problems to start with, because much depends on the attitude of the CAA inspector.
IMHO being cautious is a good thing in this case because if you get caught with your trousers down, you have a grounded plane.
pending that have the GFC700 autopliot disabled
You may need to actually rip it out, because the inspectors are well aware of the old technique of pulling the CB, putting a cable tie around it, and placarding the item "INOP"
A friend of mine tried to install 2 x GNS530 but EASA refused to approve it because, they claimed (total bollox), one could affect the other through the crossfill connection. They would not accept the removal of the crossfill connection on the grounds that they knew the owner would just put it back in
The problem we have now is that every mod (minor or major) goes to EASA to be examined and they can do what they like. It's not like the FAA minor mod regime where stuff can be done and signed off by an A&P/IA.