A few points:
I am familiar with aeromagnetic stuff as a result of having to administer one of those University R&D syndicates circa 1998 that was trying helicopter towing of a large loop of antenna for prospecting - an abject and very expensive failure (but a verrrry taaax effective project!). You are going to have to demonstrate reliable detection in Australian jungle conditions before taking something like that to PNG.
Knowing secondary jungle in New Guinea, any drone used is going to have to be expendable, you will never find it, let alone recover it, if it crashes.
For armchair critics of Mr. Billings, consider that where he is going there is not reliable (if any) 240V power, no technical resources and the official bureaucracy is mind blowing if they sense a buck is to be made out of you. The logistics of mounting any expedition in PNG are mind boggling. Anyone who has ever seen the inside of a PNG general store in a village will know what I mean.
The thought also struck me while watching a CAT D8 put in a bushfire containment line late last night was that the driver who allegedly "buried" the wreck out of tribal jealousy, probably also drove over it and crushed it because it saves him time and effort, which is a depressing thought. You may be looking for two engines and a flat aluminium pancake buried eighteen inches deep under featureless secondary jungle.
Sorry for being depressing but I admire your tenacity and wish more power to your arm.