If you were keeping the stock pistons, you probably wouldn't be increasing lift and duration enough to run into interference issues, but with the new pistons it's a lot more critical to know your clearences. Even more so if you throw adjustable cam gears into the mix. If you're putting in pistons why not go the rest of the way? You need to know what head gasket your going to run so you can use it's thickness to calculate your clearences, or make very small adjustments in static comp ratio. So........using clay is probably your best bet, it's ghetto but people have been using it for years.