Hi xin
No need to go down there you can see the Lanlivery Registers on Family Search.
https://www.familysearch.org/search/collection/1769414At the bottom of the search page is a link to browse through the images coloured red. Click on this and then choose Cornwall and then choose your parish.
The Lanlivery register is in very poor condition for the time period you are looking at.
Baptisms, marriages, burials, 1600-1758 - The bit you want starts about Image 78
Baptisms, marriages, burials, 1644-1812 - The first part of this register is obviously a re-write but it is very legible. The records are composite so the events appear year by year and not in special sections for
Baptisms Burials and Marriages.
I could not find the marriage you are looking for. But some pages are in very poor condition with damage that makes the illegible and the person who did the re-write may not have been able to read all of them.
However, even if they were perfect you would be very frustrated because in this part of the register the marriages do not state the surname of the bride. It's all John Smith and Mary his wife were married. (Unless you were the vicar's or the Squire's daughter.)
I guess Hester's surname mentioned in a Will or some other document. Since this practice of only giving the bride's forename was pretty common in the 1600's it's possible you may never find a Helliar - Leverton Marriage. There is no other information about John and Hester other than their names in the register. Except that Hester is stated to be a widow when she was buried.
There is no age at death stated but I did find a child of John and Hester's baptized 12 Sep 1686. If she was born in 1630 she would be age 56 when he was born. There is a Hester Cleverton born at Poughill but even 1633 puts her over 50 in 1686.
Hope this helps
Venelow
Canada