I think the problem with the Life Like frame is two fold. It is lighter, because there's less of it there. The Atlas frame has more meat above and behind the motor. Even after milling it out, there's a lot still there. The other problem is I believe the LifeLike frame is a hair narrower, so the shell wants to vibrate more, creating extra noise. My GP-9 chopper rides on a Life Like frame still, I'll have to do some side by side comparisons.
I did two GP-20's for the Laurel Valley, same cuts, same decoders, but the stock shells, and they run like champs.
Lee