Up-date.
Well I'm still at it. Still collecting information about the 19th century performer who has me in thrall.
Just to tie up a few loose ends on this thread:
1. I now believe my man was named -- "William Robert Barlow". Sometimes, early on, he used W. R. Barlow. Later he dropped the "William" although he was still known as "Billy Barlow".

(Oh! happy days! and there's only about a couple of hundred of them -- most of whom I've come across.

2. I've tracked down Ledger -- mentioned above.

Still have not found my Barlow with Pell's "Original Ethiopian Serenaders" except for that one reference given above in 1857.
I still have no reference to him from America. AND I still have no picture of him.
Onward and upward,
Cheers, Joy