Your new compression will be 10.8 to 1 with the vortec heads.
The spring pads will be OK you don't need to machine them for the 268 comp cam but you will need to get other springs. You will also need to machine the top of the valve guide down because any more then .450 lift and the retainer can hit the top of the guide. I would machine the heads for screw in studs and guide plates. this will eliminate the need to run guided rockers, plus your getting close to the limit where pressed in studs will work without pulling out.