So far i've tried running 767's both full face and with a cavity. They both make good power (i'm running 36* of timing), but i'm just having trouble getting the brushes to last for a run without burning up and making the motor lose a signifigant amount of power. I haven't been running a fan but i'm going to try the associated heatsink fan this weekend.
Thanks for the suggestions about the polarized brush trick, i'll have to try that.
-James