Aren't new springs needed for the 270s? The valves are opened for a longer time period and at very high rpm, there is a lot of strain on the [stock] springs. For information, the 262's are the 'street' - you can use stock springs, the 268s are the 'mild street', and then there are the 270's and 274's. The power gains increase in the series but the power is produced higher up in the powerband as you go up the series.
You don't want to do the cam install twice so call Comp Cams for their recommendations for springs and cams for your application. Their techs are there to help out and the help is free (well, it's built into the price of the cams but you know what I mean).