What parts from la 318?

He meant to keep the correct balancer that came with the Magnum engine, and mark it to match the LA timing cover, if using an LA cover with opposite side timing marks.
If the original balancer on the Magnum engine is not available, or is a one piece with built in serpentine pulley, get a used Magnum without that pulley, or get the professional products balancer and install the Magnum valance weight.