I dont think anyone will have specs on the factory amp.... but the power wires that run to it are the same gauge that runs through the whole electrical... something like 16awg.... I would be really surprised if any factory amp does more than 35rms, 50peak but this rating is just misleading since you would be hitting hard distortion and clipping... headunits in just about every flavor.. stock and aftermarket only rms from 12-20 watts
14vac X 14vac / 4ohm only yields you 48watts and this would be with the engine running.... any amp will be more power than this headunit math and just about any amp will be more than a stock amp
in any basic amp... headunit or other they are just basic power inverters and they take the 14.4 volts DC and converts it to 14.4 volts ac and then adds the audio signal... to get more watts out you would need way more inside one of those amps that you would see if you opened it up..
even in the mach 460 mustang systems from 99-04 they only had about 45rms to each speaker and there was 6 speakers... 4 full range and 2 tweeters
I hope this ramble was helpful at all.... lol