Magnum heads. Is it safe?

Seriously, disassemble the whole head naked, wash it with soap and water, dishwashing soap is good. Dove, Joy etc. since it's made for greay pots and pans. Then air dry it with the compressor.
Do what moper was saying.
Where saftey glass' and or mask.
Cut and grind in a corner, away from fire hazzards.
Have at it.
Wash again before reassembling the heads. Get into the valve guides for sure.