cam for flat tops with no valve reliefs

i have a 360 that has flat top pistons with no valve reliefs. i am running stock j heads. i am planning on getting hardend valve seats put in and some porting done. i was wondering if anybody knows how much lift i can go with my cam before i run into clearance issues. the guy i bought the car from said that i can`t go any larger than a 450 lift cam. does this sound right?

what is the easiest way to check what the cam is that is in my car?