Magnum vs LA bash!

Magnum heads are better. They have closed chambers that need less ignition timing, have dual quench areas, and less cc volume yielding more compression. The intake port although slightly smaller in cc volume flows more air = MORE PORT VELOCITY. The exhaust port is vastly better than the majority of LA heads (the 308 is very close but still not as good). The valves have lighter 5/16 stems and single bead lock grooves as compared to heavy 3/8 stems and multi groove locks for the LA, this greatly improves the engines ability to rev without valvetrain stability and durability issues. The Magnum valves have superior flow shape. The intake is a 13* nailhead with no ski jump on the back, the exhaust is a 22* tulip again with no ski jump on the back. LA valves are the opposite. Every LA head to come through the shop has needed the exhaust guides redone usually both. Magnums, never needed to put guides in one yet. Lets talk rocker arms. Magnum has a true 1.6 ratio, LA usually around 1.4. Anyone who's raced an LA motor with the OEM stamped rockers knows it don't take long before you punch a pushrod through one. Never seen a Magnum rocker fail (yet). Head cracking, being the guy who runs the magnuflux equipment at the shop I can tell you that both LA and Magnum heads are terrible for cracking. 50/50 for both families on this, . I take a beating from the Chiby guys at the shop for that all the time, if I hear one more Mopar crackhead joke I'm kickin some ***. Intake manifolds obviously the Magnum doesn't have as many choices, but the one that works best 99% of the time for the LA is also made for the Magnum, the RPM AirGap.
Short block wise the Magnum is better also. The pistons are lighter weight hyperuetectic not heavy cast. They carry 1.5mm/1.5mm/4mm low tension rings as opposed to 5/64 5/64 3/16 standard tension rings. They sit higher in the bore by about .020 " IIRC. The rods are also lighter weight (narrower at pin end) and better quality forgings. The factory block casting quality is much improved over the LA, although I've noticed they sonic check thinner. The deck height has been spot on side to side, front to back on every one I've checked so far, older LA never even close (late 80s early 90s roller blocks have all been good though). Oiling system is a little better, oil feed passage from lifter galley to the mains is bigger, oil filter plate has 6 holes vs 4 (just drill more holes). Magnum has hyd roller cam vs LA hyd flat tappet, definitely a plus. Magnums being EFI motors will usually be in good condition even with high mileage unlike an LA that with as little as 50k are in need of a ring and bearing overhaul at least. As mentioned earlier the Magnum motors seal up much better (the 3 Mag cores sitting in the shop right now are nearly bone dry).
Disadvantages IMO are that you'll need an LA front cover, a pass car oil pan/pickup, and an LA distributor.