Like mentioned above, with the stock heads the engine will be self goverened while accelerating in gear much past 6000 RPM.

Other than that the engine won't put in "more" fuel, only the same amount more frequently. The injectors would be OK, but the the fuel pump capacity might be low.

I wouldn't rev it past 7000RPM at idle however, you might get some valve float past that point, which could allow the pistons ot contact the valves. Above 7500, I'd get concerned about the bottom end comming apart.