Hello Keith, the "lump" is part of the ammonite e.g. a piece of the next worl or an impression of it.
So I would not take it off; it is part of the course ribbing that can be seen on a part of the shell.
Wish I could show a picture of my specimen, but it seems to be impossible for me to upload photo`s on the forum, perhaps I will ask a friend to do it for me.
"The big fall" was at Port Mulgrave, going north, if you go there the scar on the cliff is still visible and if I am not mistaken there is another happening, just a little distance furter north.
the search is as valuable as the finds...