What are everyone's thoughts on these? I am going to a t56 magnum soon and want some input as there seems to be a lot of controversy over this. I will be using a quicktime bell housing and as much as I don't want to do it(because the engine will still be in the car), I will be dial indicating the bellhousing to ensure it is within the spec of .010" concentric alignment. What would be best in my situation? I am running a 489 mark iv big block. Also does anyone have a part number for either? Thanks!