roller cam or flat tappet?

i have a 408 stroker shortblock that iv ehad for a while. but i dont know what cam i have in it. how can i tell if its a roller or flat tappet cam. it never had the lifters in place. asking because i ordered edelbrock heads with the double springs. says its for roller cams only. should i just order a new roller cam that best fits my setup? i dont know lift, duration for this cam. thanks