You can get new magnum heads from EQ. They outflow the originals and are thicker in the area's prone to cracking. Check out ebay for them.
Magnums offer more potential and tolerance for shitty gas than the la head.
But it's more money as you either need a magnum intake/valve train or drill the heads for la intake pattern.
You need more than just pushrods to put on a magnum head. Magnums use a specific head bolt also. La valve covers will work but the magnum ones are less likely to leak.