Magnum serpentine

In order to use the Magnum serpentine accessories, it's necessary to use the Magnum heads, as they are the only heads that have the correct bolt hole placement for the Magnum accessories.
In order to bolt the heads on an LA engine, you'll need custom length hollow pushrods (Magnums oil the valvetrain though the pushrods) and, possibly, AMC lifters, depending on if you use an aftermarket cam with lifters that have the pushrod oiler holes, or not.
Most do, these days.

You'll need everything, the timing cover and all.
If you do this, there are a couple intakes on the market to convert from the tall "kegger" intake to a more conventional intake, or you can drill and tap the heads for an aftermarket (or stock) LA style intake.

It's not really a cheap conversion.

IMHO, you should just buy a Magnum 318 or 360 and get it over with.
Oftentimes you can buy an old '92-'95 or so van for not a lot of $$ and have the whole conversion.

Mark.