There are threads on this issue here. As mentioned, there are have been drilling guides fabbed up to redrill and tap the heads for the LA angle intake bolts. Also the Engine Quest magnum heads are obtainable predrilled for the LA intake (CH318LA) (Hughes sells them under their own brand).
There are a lot of Magnums out there running LA intakes.
I have the EQ heads and have run the LD4 as well as the Performer intakes on it.
Craig