Compu cams XE268H question

so Barry, you installed this cam and didn't change the springs on the 340 x heads. If I have to change the springs and buy a kit with all that stuff in it, I may as well go big right. how big can I go and not have to change pushrods or rocker shafts. I have a 509/292 in my 440 Duster. that is what he would like. something like that. would the 508/292 small block purple cam work in this 360 with just changing the springs.