To teach for an IR you have to have the IRI qualification, that has nothing to do with being an FI(R). The only question is whether you can complete this qualification on the basis of 200 hours under IFR or 800. Under the JAA is was always considered that 800 was necessary, but I can find nothing specified in Part FCL that requires you to have 800 hours if you are an FI. An FI(R) is an FI and it is not one of the limitations stated in FCL.910.FI FI — Restricted privileges.