Normally not a problem. The 1/10 scale brushless Arrmas (and maybe 1/8 too?) come stock with them. Check the specs on the esc you want to use to make sure though. The voltage your pack puts out (i.e. the type and cell count) plays a pivotal role in motor selection (kV) and appropriate final gear ratio, so be sure to account for that. You should also try to pick a motor and gear ratio that will work well, or can easily be converted to work well, with 2s lipo. It is not a question of if but when if you know what I mean.