stop_the_beast
I forgot to mention in my previous post that the center outlets are different between the LA heads and Magnum heads.
If you are using Magnum exhaust manifolds with LA heads, you should definitely spend a few minutes with a grinder doing a gasket match on the exhaust manifold as the center ports are raised and seperated. Not like the siamesed center ports on typical LA exhaust manifolds.
Better yet, use a set of Magnum heads. Definitely the best bang for your buck... closed chamber (means higher compression ratio), swirl ports, better flow, lighter valve train. If using junkyard heads, get them off of a 5.2 engine. The heads are exactly the same between 5.2 and 5.9, but 5.9's were run a lot leaner for emmisions requirements and this makes them more likely to be cracked between the valve seats.
If you do the Magnum head conversion on an LA block, there are two things you need to do;
1) Special pushrods, typically 7.625" to work with the stock Magnum rockers
2) Either use a Magnum bolt pattern specific intake manifold (or dual pattern manifold) or redrill the Magnum heads with the LA bolt pattern. See this link for more details;
http://www.bigblockranger.com/Magnum.html
Mike Bynum