adding magnum 360 parts to la 360??

Yup. Do a search here first. Swapping mag heads onto an LA is well documented

The EFI will be a bit tougher. You have at least a complete underhood harness and all the parts?

What about the flex plate / pickup for the crank? Using a new OD trans you will have to modify the rear crossmember and chop up the floor. This too has been covered on the internet, search for that.

A couple of guys have modified the "beer keg" intake for better performance. I think if I was doing something like this I would consider dumping the keg and getting an aftermarket EFI manifold, or modifying one.

For the computer, if you don't have one it MIGHT be easier and cheaper to go with a Megasquirt.