Magnum heads have rocker oiling through the lifter/pushrods instead of through block and head passages like the LA.
It can be done if you use lifters and pushrods (custom length, too) that have the oil holes. Then you will have to get a Magnum-specific 4 bbl. intake (unless you get heads drilled for the LA pattern or have it done) and throttle linkage, and then compensate for the different 1.5 (LA) vs 1.6 (Magnum) rocker ratios when selecting your camshaft.