Thanks for the response. FWIW, the attached Specification page shows the GT engine (the Hurricane) making 268hp on premium fuel. The specs show the R/T engine (combined ICE and elec.) making 288hp, with no mention of fuel requirement.
Update: The full Owner's Manual (p.266) states that the 2.0 engine in the GT is designed to operate on 87 octane gas. However, "optimal performance" requires 91 octane or better."
There is no mention of the fuel requirements of the R/T because that model is not covered in the manual.