I found a new clue, and so wanted to try this again.
Simon de Montfort VI Earl of Leicester, was one time Lord of the manor in Lapworth, Warwickshire ( "in 1265 Simon de Montfort, Earl of Leicester, held the manor of Lapworth"; from Dugdale, found at 'British History Online'. )
I am in possession of an English charter, undated, but attributed by 'experts' (previous auction house, and Robert Hudson, "Memoirs of a Warwickshire Parish", 1904) to about 1220-30. The U. of Toronto website dating algorithm puts it somewhat later, perhaps 1250-1270.
The many Simons de Montfort were known by a few names, one of which was "Simon de Montfort-Lamaury, or "de l'Amaury", in reference to Amaury de Montfort, son of Simon I.
HERE is the name of the grantor as it is spelled out in the document. This is 400dpi, so enlarged quite a bit.
"Limbure" and "L'amaury" seem to be very similar in pronunciation.
If:
-charter scribes spelled many names phonetically
and
-Simon de Montfort/L'Amaury was tenant in chief at one point (virtually contemporary with the charter)
Then, is there any logic to thinking that the "Simon de Limbur(e)" of the document, who is making the grant, is "Simon de Montfort" or (de Monfort d' L'Amaury)?
Thank you again.
Unfortunately, the one thing that final letter is not is an 'e'. It is an 's', and probably a 'us' or, even more likely, 'is'.
It is hard to tell without looking at other letter-forms in the same document, but my best guess from the data available is "de Limbirris".
You would have a hard time arguing for l'Amaury, I think. While 'i' and 'e' are frequently interchangeable, 'i' and 'a' are not. Moreover, since the scribe is writing in Latin, he would have no need for the French pronoun le or la. If he did, that would still point to the the toponym being Imbria, that is, Fehmarn in the Schleswig-Holstein.
It's much more likely to be "Limburgum", the Latin toponym for Liège in Belgium. 'urg' to 'irr' is a very easy and common sound-change.
Edit: I just checked with a friend who holds a certificate in paleography from UToronto, and he confirms that the most likely readings are 'limburis' or 'limbirris'.
Double Edit: I would trust the Toronto dating. Auction houses always put the earliest date they can reasonably justify (and then sometimes take a half century off that) to increase the price.