Gwennanmay, my ancestors were in the 1861 census and they lived in what is now called Cwlach Street but I don't think that it had that name then.
It appears that the Chapel House was wrongly named in the census and was not Zion but should have been Caersalem.
Just so that you can check for yourself have a look at the Census records for your ancestors again and to confirm that the info I have supplied is correct I have listed the names of some other properties in the street:-
Ty Glas, Troed Y Rhiw, Pendyffryn, Ty'nymaes, Tygwyrdd, Penyfron, Frondeg.
They are near Caersalem Chapel House and some of those properties are still there today. I would be interested to know if you agree.