Looked in the papers first and came up with
Oxford Times 01 October 1864
Strickland-Liddell.-September 24, at St. Andrews Church, Holborn....William Stokes Strickland, to Emily, second daughter of Robert Liddell, late of St. Clement's, Oxford.
So think this death could be worth checking as is age is a bit up and down
Oxford Journal 20 February 1875
Feb. 12, at 20, West-street, Bristol, Mr Robert Liddell, aged 73, late of this city.
1871 census in Gloucestershire
https://familysearch.org/ark:/61903/1:1:V5YM-WBZRobert Liddle Lodger Joiner 66 Northumberland....no family
1871 Alfred in Gloucestershire, marries Clara Young 1874
https://familysearch.org/ark:/61903/1:1:V5YM-Q771871 Found a Frank Liddell born Oxford c1852....Railway Porter
https://familysearch.org/ark:/61903/1:1:V5TM-671You would need to access a pay per view site for Alfred's marriage, Frank Liddell is a witness, father Robert, carpenter.
If you have a copy of Frank's marriage, you could compare signatures.