Hi Ann,
I would agree with Nicky that they are probably your couple. I also came another possible marriage entry: (freeBMD website)
Marriages Jun 1870
HAMMENT Matilda Docking 4b 511
Morley John Docking 4b 511
WAGG Susannah Sarah Docking 4b 511
WINSBORROW George Docking 4b 511
(Docking is not so far from Lynn)....but I think you can eliminate Susannah Wagg as a possibility as I also found the following entry on the 1881 census:
George MOULHAM Head M Male 37 Castle Rising, Norfolk, England Butcher
Harriett MOULHAM Wife M Female 38 Heacham, Norfolk, England (Wife)
Ernest MOULHAM Son Male 5 m Heacham, Norfolk, England
Emily WAGG Sister In Law U Female 43 Heacham, Norfolk, England Housekeeper
Susanna MORLEY Sister In Law M Female 40 Heacham, Norfolk, England Independent Ministers Wife
Flora MORLEY Niece Female 4 Cowlinge, Suffolk, England Independent Ministers Daur
Ernest MORLEY Nephew Male 3 Cowlinge, Suffolk, England
Susanna CLAXTON Serv U Female 17 Heacham, Norfolk, England General Servant Domestic
Emma STAMPS Serv Female 13 General Servant Domestic
Mary Ann BUXTON Lodger U Female 75 Yarmouth, Norfolk, England Interest Of Monies
Snettisham Rd
Heacham
Norfolk
RG11/1991 Folio 71
On the freeBMD there are also some possible birth entries for Susannah:
Births Sep 1838
RANDAL Susanna Blofield 13 24
Births Dec 1844
RANDELL Susan Downham 13 77
Births Jun 1848
Randell Susan Wisbeach 14 190
Births Sep 1848
RANDALL Susan Downham 13 92
The Dec 1844 entry in Downham (Its also quite close to Kings Lynn) fits best with the 1851 census details that Nicky found, although Susanna seems to have been a bit confused about here age over the years so who knows

Regards,
Emily