I guess, you mean scale 1/100. That is a bit complicated, since the casting would consist of about five to nine parts (body/wing + engines) and the body length (70cm) exceeds the max frame of the mould. Also the large diameter of the body would probably give an uncontroled level of heat and metal deformation when cooling down. In this case you must mould a hollow sectional body, which is impossible for us because of toolings.
These models are all full aluminium bodies.
In other words: 747 is too large!
I recommend to search for an old aluminium display model from Verkuyl or Fermo being in not perfect condition anymore and to restore it. In this case even the price would be similar to a re-casted one.
I did the same with the below shown Verkuyl 1/100 747. It's fully restored.