magnum or not

They started putting roller cams in the LS engines in the late 80's.

What do you mean by bottoming out valves?

The stock valve springs can not accomodate much more lift than stock before they bind and any performance cam is going to have more aggressive profiles than stock so you really should be looking at new springs that are recomended for the cam you plan to use.

The next thing you have to worry about is the spring retainer bottoming out on the top of the valve guide. Not sure on the LA head but this happens a little past .525" of lift on the magnum head. It is easy enought to correct by machining down the guide.

Stock pistons are far enough down in the cylinder that any lift that would be practical for the air flow capabilites of the head won't hit. If you are zero decking if you are going over .525 lift you should check and verify the clearance.