Rockers, non adjustable

Its not impossible to have your lifters "drain" overnight or after sitting for an extended period of time although this isn't ideal. Turn on the car and let it run for a minute or two (Only want to circulate the oil a little not warm up the car) and then check again. If the rocker shafts are tight then there should be no noticeable play in the rockers

If you have the correct pushrods and after running it everything still feels loose then you might want to pull the valve covers and the coil wire and let the starter turn the motor while you observe the valve movement. If you notice that loose rocker arm not move at all or move very little then inspect the cam to make sure you didn't wipe a lobe