if you have play on both cranks it's probably the bb. did you put the time into adjusting it when you put it back together. there should be no play on the spindle. another option is that something in your bb is shot: did you replace the berrings when you rebuilt it? if not, did any of the berrings look pitted or damaged in any way? were the berring grooves in the cups nice and even? if your berrings come in a 'race' holder thingy was it bent or otherwise mutilated?

oh, and just because flamewars are such fun: did you put jis cranks on an iso spindle? (ducks and runs)