Hi Matt
We can see those Sussex microfilms via the LDS catalogue on Family Search
So we look to see what Sussex probate records they have (in the same way as if we were planning to view or order them at a FHC)
England, Sussex - Probate records (39)
then select -
Wills, 1534-1700 Diocese of Chichester Consistory Court
we needed -
Original wills (STC I/II) 1684-1690 British Film 1068641
to the right is a camera icon, which means that we can view the microfilm online
Having got the microfilm up, we then have to find what we want ourselves!
All this is fine for microfilmed images of original records, but it seems that they wont let us see modern day transcriptions of anything (you have to be a member or at a FHC)
They have some inventories on there, if there was one for Caleb then I don't think it's available online (no camera icon)
There's a Chichester Consistory Court index on findmypast, which said that Caleb's will had the reference
STC I/27/355b. Which was a bit of a help in finding it in the sense that I landed on a will in 1682 which the index said had a ref of 335b, and Caleb's will was indeed twenty or so images further on.
The Keep website is good for getting the necessary details for East Sussex wills.
I guess if they have a particular microfilm at the London Family History Centre, then they should be able to make a copy of what you need.
John