@MJA Chaser: Thanks for the link, I've had a look at the video on the MDX search and from what I glean from that there's no indication that the equipment isn't working as they would hope. I have also located some useful data on the equipment shown, this may be the portable device they're using however.
You may have further inside detail though? Has the search been completed? Any idea on testing they carried out prior to the survey?
@Sunfish: There's a reasonable amount of material in a Wasp engine, as well as the ancillary mounts and other gear pertinent to the aircraft as a whole. There are possibly two engines in close proximity, although that may not be the case depending upon what aircraft it actually is, what happened at the time and any intervening 'works' that may have occurred. In any event I'd like to think there's sufficient to detect at the sort of distances we're thinking of. The magneto's would assist insofar as they add to the mass of material, but they're not likely to be instrumental in anything - particularly not at the range this is likely to be at.
@David Billings: As I write I'm looking at a LiDAR survey of one of my properties. It shows the ground contour as one would expect, but it does not show objects upon the ground. This is most likely a higher-level survey than you're considering but, particularly if the craft is buried, I think the best you could expect would be (as you say) to locate the 'dozer workings and hope that leads you to the area you'd like to inspect in detail. I'm doubtful you'd get much more?
I hope to have a little time today to further some research, if anything comes of that I'll post the detail.
FP.