Best you start taking SITHNEY seriously I think.
Firstly, I just checked the Sithney OPRs and the marriage of Oliver and Elizabeth was certainly 1765.
Now - I am now about sure that the Oliver ALLEN who married Mary HUMPHRIES was from Sithney.
Oliver ALLEN m. Elizabeth RICHARDS 1st May 1765 at Sithney
Both were then 'of Sithney'.
I have checked for marriages of an Oliver Allen to Elizabeth and IGI gives only two results - this one in 1765 and another in 1732 which would be just a little bit early.
So I think you have to live with what I am about to give you.
The Sithney OPRs show only two children for Oliver and Elizabeth after which this couple ends up in Ludgvan.
So here is the line up I have found of children to Oliver and Elizabeth:-
OLIVER bp. 2nd February 1766 Sithney
Elizabeth bp. 24th May 1768 Sithney
William bp. 21st October 1770 Ludgvan
Richard bp. 30th April 1775 Ludgvan
Elizabeth bp. 11th October 1778 Ludgvan
Susanna bp. 2nd December 1781 Ludgvan
Elizabeth bp. 5th December 1784 Ludgvan
OLIVER m. Mary HUMPHRIES 26th December 1789 Ludgvan
Richard bp. 19th October 1828 Towednack
William bp. 5th December 1830 Towednack
John bp. 11th March 1832 Towednack
Elizabeth bp. 29th September 1833 Towednack
Mary Humphrey bp. 30th April 1837 Towednack
Joseph bp. 22nd July 1838 Ludgvan
Thomas bp. 20th May 1840 Ludgvan
John bp. 24th September 1843 Ludgvan
Grace bp. 6th December 1846 Ludgvan
In the 1841 Census the family is at Newtown, Ludgvan.
Richard and Elizabeth both age 35
Richard 12
Elizabeth 8
Mary 6
Thomas 1
In 1851 they are at Crowlas
Elizabeth 43 widow
William 19
Jane 17
Mary 15
John 8
Grace 4
I don't know where William was in 1841.
And in 1851 we have JANE where ELIZABETH possibly should be.
Unless Jane was baptised somewhere other than Towednack or Ludgvan.
Also, in 1851 all are recorded as having been born in Ludgvan which is possible even though some, like William and Mary, were baptised at Towednack.
Richard (bp. 1828) was married to someone named Mary by 1851 and was then living at Liskeard.
Returning to OLIVER who married Elizabeth RICHARDS at Sithney in 1765.
It looks probable that he is the following
Oliver s/o Oliver & Thomasin ALLEN bp. 4th April 1742 at Breage
Oliver ALLEN m. Thomasen PAIN 2nd December 1734 at Breage
The only other option for this Oliver is that he was baptised at St Cleer which is way on up towards the Tamar River!
Before I finish off I will try to identify Richard ALLEN's wife Elizabeth JAMES.
Looks like she was born about 1807/8 at Ludgvan if we go by the Census.
The only possibility looks to be:-
Elizabeth d/o Joseph and Sarah JAMES bp. 13th October 1805 at Ludgvan.
The next possible was actually born in 1810.
And the only Mary HUMPHRIES baptised at Ludgvan appears to have been Mary HUMPHRY in 1692 so we need to look elsewhere for her.
Time to close for a while.