Forgot to say that there's a photo and an engraving of Bethlehem Church & graveyard on GENUKI. Graveyard doesn't look very big or maybe that's only part of it.
I don't know if Lancashire Family History & Heraldry Society has done or published transcriptions or a plan for either location.
There isn't a burial register for Bethlehem Unitarian Church in Lancashire Archives, just baptism and marriage registers. Church registers guide for Non-conformist churches is a pdf in alphabetical order of place.
You say that you have grave numbers. Are they for Bethlehem or the cemetery? If Rawtenstall Cemetery can you work out which section they are in from the plan on LANOPC?
Perhaps if you post some names + dates?
Just seen Pauline's post.