Was 'help' pronounced starting with a vowel sound?
In early Middle English, people used an before all words, whether they started with a consonant or vowel. They started dropping the /n/ before consonants, but the /n/ was retained before /h/ longer than it was retained before other consonants.
Shakespeare seems to use "a" before almost all one-syllable words starting with "h" except ones where the "h" wasn't pronounced, like hour, heir, herb, host. (A horse! a horse! my kingdom for a horse!). However, the King James Bible, written around the same time, doesn't seem entirely consistent in their treatments of "a/an" before /h/. There are 70 instances of "an house", and 5 of "a house", in it (and 6 instances of "an horse", and none of "a horse"). Keeping the "n" was presumably thought to be the more formal way of writing things, probably because it was older.
I think it's very possible that by 1729, nobody said "an help" anymore, and that Edward Wells wrote "an help" solely because the King James Bible did.