Not many choices for the magnum
M1 dual plane
M1 single plane
Eldebrock air gap
Cross-wind
Hughes will drill you heads for $80.00 and then you can run any LA intake.
I made a jig to do mine, its not pretty but it worked great. I had maybe $10 in it. Now I can use both styles of intakes. Oh, I already had a 5/16 drill bit and a 3/8-16 tap for the bolts.
Here's mine. It's a little (ok, a lot) more robust than it needs to be, but I wanted to be able to use multiple times. It even has removeable bushings so the drill bit doesn't wear the bores out.