Yep, using a pushrod that is as long as possible will give you more valve lift. But you have to watch out for the gotchas. For example, with Harland rocker arms on my 470 I toasted the pushrod ends since the long pushrod puts the cup out of reach of the oil squirt. Pushrod oiling solved that problem. With T&D rocker arms you have to have the adjuster in the correct location or else they won't oil. So you can't screw the adjuster all the way in or all the way out, it has to be in the middle of the range or else you'll kill the rocker arms.

This trick is also dependent on the design of the rocker arm. If you get a bunch of different Mopar rocker arms and put them on the same shaft you'll see that everyone designs their rocker arm differently. So the angle of the backside of the rocker arm is different. The pushrod to rocker arm angle can vary a lot between different rocker arms so the long pushrod trick may or may not work.