Magnum heads on LA block

I put EngineQuest magnum heads (factory replacement head) on an LA block, with flat tappet cam. They offer a magnum head with LA intake manifold bolt pattern and LA style thermostat bypass hose. Everything fit great.
The magnum heads use 1.6 rocker ratio that puts the top of the pushrod closer to the rocker stud/pivot point. I did a little clearance grinding on the heads/pushrod holes with a carbide cutter to clean up casting flash, not because there were any problems. I had no issues with pushrods close to or contacting the heads.

I would do a mock up of your engine with cam, lifters, pushrods, heads/rocker arms/valves with checking springs, and verify clearance. That is what I did, and as said had no problems.
For rocker arms I used CompCam stamped rocker with roller tips. They are cheap and said to be bullet proof. Do what you want of course.
I did need to run small block Ford/Oldsmobile rocker studs so the ARP polylocks would have enough (correct) thread engagement to lock the rocker arm adjustment in place. Hope this helps.
Here is a write up I did on the head build:
http://www.forabodiesonly.com/mopar/showthread.php?t=180777&highlight=enginequest+heads