Magnum Block Education
This website is a very good read
http://www.magnumswap.com/using-la-parts-on-a-magnum/
I don't know what you mean "early and late" all magnums oil the same. You may be confusing LA with Magnum
There's an adapter made for the magnum cam to restore the fuel pump, and you can use the earlier LA timing cover
You cannot put LA heads on a Magnum, but you can (with the right parts) put mag heads on an LA
LA heads are shaft rockers, oiled up through the block and through the shafts
Mag heads are oiled through the lifters/ pushrods like a Chev / Ford "ball stud" rockers