My reading of the regulation is that as the holder of an FI rating who is qualified in that class of single engined aircraft, then you are qualified to instruct on it. I suspect this is not the intention of the rule, but that 's what it says!
The privileges of an FI are to conduct flight instruction for the issue, revalidation or renewal of:
(b) class and type ratings for single-pilot, single-engine aircraft, except for single-pilot high performance complex aeroplanes; class and group extensions for balloons and class extensions for sailplanes;