KGarrad and MargP,
Thanks for the replies. I should have mentioned in starting this thread that I'd done some investigation of various Dallow possibilities (see my thread below titled Dallow for the details on the way this played out). I was actually pretty much convinced that the Fownhope Dallow family mentioned here was my line. One reason was that, though I could find no matches for Thomas Dalley connected to Fownhope, I found Thomas Dallow, and he shows up again in the 1871 census. So, it seemed more than a coincidence, that my Thomas Dalley seemed absent from the 1861 and 1871 censuses, while Thomas Dallow appeared in both. Moreover, Fownhope seemed to be a very small place, and this increased my confidence in the equation Thomas Dallow = Thomas Dalley.
Then I sent for the birth certificate mentioned here, Hereford 6a 456, 2nd quarter 1854. The person identified is Thomas Dallow, born 20 Apr 1854, Bye St. St. Peters, to Thomas Dallow, Postman, and Caroline Dallow, late Caswell, formerly Carpenter.
It appears that the Thomas Dallow in this certificate is not the Thomas Dallow in the Fownhope family, and both families appear separately through several censuses. In addition, it doesn't seem that the Thomas Dallow of the birth certificate is my Thomas Dalley, because I find a good match for him living with a widowed Caroline Dallow (mother) in Croydon Surrey in the 1881 census. Birth dates for both are consistent with earlier records.
Back to the Fownhope Dallows. It looks like Ann Dallow married and was widowed fairly quickly, then married a 2nd time to Joseph Dallow, who died before the 1861 census. If Joseph Dallow is correctly identified as the father of this Thomas Dallow, as I think is likely (not certain, just rather likely - see Dallow thread), then he's ruled out as my GG grandfather, because the marriage certificate of Thomas Dalley and Bessie Westacott gives his name as Thomas.
So that's as far as I've got in starting the search again. I haven't ruled out Dallow or any other variant of Dalley. At the moment, though, it appears these two Dallow candidates are not the right ones.