The title Reaper Man parodies Alex Cox’s 1984 cult movie Repo Man.
More accurately, Repo Man itself is a pun on ‘reaper man’, a very ancient name for Death (compare also e.g. ‘the grim reaper’). But apparently Terry has said elsewhere (i.e. not on the net), that his ‘Reaper Man’ was indeed meant as a pun on the movie-title (much to the chagrin of his publishers, who would have probably preferred it if he had called it Mort II).
The ‘Bill Door’ sections of this novel have many parallels with classic Westerns, e.g. High Plains Drifter.
If you liked the idea of the trolley life-form, you may also want to check out a short story by Avram Davidson called Or All The Sea With Oysters. It’s all about the life cycle of bicycles and their larval stages: paperclips and coat hangers.