Hi
I've been wondering exactly where it was (is!) The map link is also a great help.
They do have some manor records on FamilySearch, but sadly not Allington.
Another will - a PCC one. On ancestry
as detailed on TNA
Will of Francis Killingbecke or Killingbeck of Ardingly, Sussex
Date 15 April 1653
PROB 11/230/7
Had a quick look last night and I thought it is actually the one that originally went through in 1747?
With a related record
Sentence of Francis Killingbeck, Batchelor of West Hoadley, Sussex
23 November 1747
PROB 11/758/152
My memory of it is that Francis bequeaths Beachwood to Elizabeth, then she died and it became an administration with will annexed in 1753 to mother Mary (there is a note). But I may be wrong about all this. I'll have to give it another look!
Lack of Baptisms
We have some Siffleet marriages and (a few) burials, but no baptisms for the period we need them (there are some later I believe)
So I tend to the view that the Siffleets were nonconformists (there aren't even any Soper baptisms in Henfield?)
However, FamilySearch coverage of Sussex is not complete and, as Barbara said, the Sussex FHG indexes are more comprehensive.
Have realised FS don't have Isfield - although burials are indexed elsewhere. They do have a film with transcriptions of marriages, from which the entries for Thomas and John have been taken
https://www.familysearch.org/ark:/61903/3:1:S3HT-D447-Z9K?cat=1197887John