The most useful references here are, in the Database (Digital Tradition):

Helston Hal an Tow

and in past discussions in the Forum:

Lyr Req: Hal n Toe
Hal An Tow: notes?
Want first verse to Hal an Tow

The Cornish text given in Kennedy's book is a modern translation into Cornish of the traditional English-language song.  There isn't a great deal of variation in the song because it's associated with a specific place and annual event; only in recent years has it been sung (by revival performers) outside of its traditional context.

Malcolm