In the Banks Islands and New Hebrides the word used is merely 'dead man,' such as tamate or natmas. In the Solomon Islands a very common word in various forms is tindalo. The question again occurs whether these should not rather be called gods. There are certainly some to whom prayers and sacrifices are offered, whose place and time in human life are forgotten or unknown, and whose existence as persons possessed of powers far superior to those of living men is alone present to the belief of the existing generation. Such may not unreasonably be called gods. But, whereas in the Eastern groups such beings are plainly called 'dead men,' it seems more correct, and serves better for clearness, to use an English word which shows them once to have been living men, and separates them from any such beings as are believed never to have belonged to human kind. The word 'god' cannot be a translation of 'dead man.' Where, as in the Solomon Islands, a distinct name, such as tindalo, is in use, this objection to the use of the word 'god' does not so plainly apply. Yet the natives emphatically declare that every tindalo was once a man, that the tindalo is the spirit (tarunga) which once was the seat and source of life, intelligence, and power in a man who was then in the body. The living men who worship the tindalo regard themselves as possessed of that non-corporeal nature which alone remains in the dead, and is the seat of the dead man's superhuman power. They believe that some of them have a measure of that power, derived by them from the dead. They believe that, when they are dead, they will also, it may be, receive a great access of this power. The difference which they recognize between themselves and the tindalo is that they are alive and have but a comparatively small measure of spiritual power. But it should be understood that every living man does not become a tindalo after death. The large majority of men are of no great importance, and show no remarkable powers in their lifetime; alive they are nobodies, and such they remain when dead. But there are always some living men who show qualities which give them success and influence. Such success and influence are not ascribed by the natives to natural qualities, but to the possession of that spiritual power which they have obtained from the tindalo with whom they live in communication. When a great man dies, it is expected that he should prove to be a tindalo, a ghost worthy of worship, an effective helper, one whose relics will put the living in communication with him. Thus, after the death of Ganindo, a chief, a famous fighting man of Florida, his name was invoked and a sign of his power sought from him. On proof of this power a shrine was built for him, his head, his tools, and his weapons were preserved in it, and sacrifices with invocation were offered to him there. Such a one might, indeed, appear to European visitors to be a god; but to the natives of the place, who now worshipped him, and among whom he had lived as one of themselves, it was his ghost, in the common English sense of the term, who was among them.
[Note: The "Florida" referenced here is one of the Solomon Islands.]
I can’t imagine that the coincidence of name and attribute as vengeful disembodies spirits is entirely a coincidence. However, I can’t find any reference to where Long got the idea or the name for his creatures. Given how common the tindalo (plural: tindalos) was in early twentieth century popular anthropological literature, I would think this must be the source.