Either way, you will be overdriving the crap out of either amplifier. And while AM is more "forgiving" as far as how you might sound on the air, with either amplifier, you are going to be over driving it way past compression and saturation and creating a mess of junk out to the antenna. The dave made will handle it better because of its no bias design it might let you get away with it.
As far as turning down the 2970n2, to reduce the carrier that much and have it "swing" up that high is definetely creating distortion already. The positive peaks will be way too high, and the negative ones happen to be approaching "zero" for a finite amount of time during voice peaks. More splatter and distortion.
The proper solution would be to have the internal amplifier on the 2970 / 2970n2 put on a switch (which is easy to do, basically just inline with the wire going to the relay on the PA (power amplifier) board so it is running without the amplifier, then go with a DX500. Nice, clean output for the most part, everything will last forever and work right. If you ever get rid of the amplifier then you can turn the one in the radio back on.
If you *INSIST* on using the amplifier in the radio, then go with an 8 or 12 transistor amplifier. Even then, it's a bit much for the 8 transistor, but if the radio's AMC and ALC are intact and limiters haven't been removed or yanked out or played with, the ALC can be set to about 100 watts, the carrier to about 25 watts, and AMC for about 100 watts peak on AM, it will drive an 8 transistor amplifier nicely without splattering down the road and trying to squeeze every last watt out of everything.
My way of thinking is, if I want more power, get a bigger amplifier. I don't think I have ever burned up an amplifier, gone through tubes, or destroyed finals in my gear in the past 25+ years I have been playing radio.