nothing that I'd guarantee, but these are the only ones that look at all likely.
Jockey St, Swansea HO107/1426/7 folio 38 pg 17
Martha Davies 45
William 30
both not born in county
Wind St, Swansea HO107/1426/1 folio 37 pg 22
William Davi(e)s 23 traveller
not born in county - name not entirely clear and I did wonder if traveller meant he was just passing through, but there's another one a few houses away, so possibly it means salesman of some sort.
I had a look at Llanelli as well, but the only Williams of about the right age appeared to be married. With no relationships given, no places of birth, usually only occupation for head of household and ages rounded down, it's very difficult to spot someone with a common name. Again in Swansea, there's a better fit for age but that William looks to be married and I assumed you'd have said if the cert had widower for William.
If you want to check where these streets are, go to Mulitmap.com and for Wind Street try postcode SA1 1DE - it's the continuation of High Street, other side of Castle Street.
For Jockey St, use postcode SA1 1NS and you'll see it's no distance at all from High Street and could have been longer before the railway line was built - High St station opened 1850.
Nothing concrete I'm afraid, but they're in the right area.
