The bosses on the end of the Magnum heads are all on the same plane... on LA heads, the bosses are on different planes (for a visual, you can probably stand a Magnum head on it's short end and it will stand, but try that with a LA and it will be precarious or impossible). You may need lots of washers to shim the Magnum brackets on the LA heads, which may or may not be stable.

Scott B. "I'm a self-made man... I started with nothing, and I still have most of it!" 68 360 rusty B'cuda 'vert (GO Fish)13.59@ 98.72 mph 69 340 GTS stock 14.18@ 95.60 mph 01 5.9L Ram 1500 Quad Cab 4x4 01 3.5L 300M 16.23@ 86.97 mph