Rozza,
Is there any link between the tune of the hymn and 70? Nigel Hudleston who recorded Pearson singing it always said the tune was a slowed down version of Jingle Bells. As Delf mentions no tunes on his sheets we can presume the tune was added later.

Somebody sang it at a session I was at last night with the extra verse and a highly individual version of the tune which went quite nicely.