That's what I said above...the oiling in a Magnum block doesn't work the same way. Magnums oil through the lifters and pushrods like other domestic engines. If you bolt the heads on, they'll physically go on, and bolt down if the proper hardware is used, but you'll have no capability to oil through the rocker shafts, unless you're a very good machinist and can drill a hole from the deck surface perfectly down to the #2 and 4 cam journals...
In short...just not worth it...are you tied to the Magnum block? There are good heads available aftermarket, or do you have W2 heads and need an LA block? Either way the parts are available...