"cully-and-twang" was very old slang for a whore and her customer (in reverse order!). A "twangman" was more than likely her pimp. The other explanation you hear is that "twang" was a kind of toffee sold in the street - but I haven't seen any evidence of its use.

The "Billy-in-the-bowl" phrase for a legless beggar was common enough, alright.

Regards