Many thanks for sticking with this thread. :-)I'm just making a further note here, in case others find the name via a search.
I've almost come to the conclusion that Richard Clarke c1831 and Alfred Clarke c1834 were indeed born to Eliza Clarke before her 1839 marriage to James Hart, and that in 1841 when the census enumerator visited the household of the widow Mary Hancock Clarke 61 (mother of Eliza) and George 21 youngest brother of Eliza, he counted James Hart 35 and Eliza Hart 36, and children Richard 10, Alfred 4, and Harriet 1(all as Hart) (HO 107/67/3).I have been able to follow Alfred's life including his reversion to the name Clarke, and his marriage etc.I think Richard followed the same pattern and was the Richard Clarke of the 1851 census being a lodger with Sarah Ann Pooley in Cambridge.I also suspect that the same Richard had a six month sentence in 1850 and a 7 year transportation sentence in 1851 (a few months after the census) (Fulbourn Chronicle notices) although like many in the 1850s, the act of transportation never occurred and he was released sometime before 1856.And, wishing to hide unpleasant facts (illegitimacy and/or prison) in Australia he chose to name his mother as Eliza Hancock (his GM's maiden surname) and his father as John after his uncle John Clarke perhaps (or some other 'john').
Noted here just for the record. Supposition, of course, in some places in lieu of facts not found.
Of course, the most annoying thing is that I can't find Richard's baptism anywhere although I found Alfred's.There are some newer transcripts of the entire Cambs county being released, and I will try to look there.