If you WANT to learn to lead - go ahead - have a ball! It's fun & not hard. JUST DON'T SAND IT - or you'll breath in the dust AND DIE!
BUT: you certainly don't need lead there - or anywhere else. Not a single quality body or resto shop uses lead anymore unless either asked to or if someone (like TopCat) really likes to. Not GoodMark's certified shops, not DealerShip shops, not any you see in magazines, not any - period. Also, you HAVE to weld those seams, so I don't know what TopCat means by heat being a problem. Once you get the lead out (torch and wire brush - don't grind or sand!), you would drill out all the spot welds and then drill holes in new quarter to weld 'em up through those. Once done you don't even need fibreglass-type bondo (KittyHair). Rage - or any - lightwieght filler will be fine. It will never crack, never pop out and never go bad - unless you didn't weld it up properly underneath.
So again, if you want to learn to lead and use it - great, have at it. BUT, don't let anyone tell you it's the "only" way or the "right" way. It's just not. If you don't believe me, go poll all the top shops in your city.