It is tough to value the Lorca without seeing it. In general guitars as collectables tend to place less value on the age or historic nature of an instrument. That is the reason that a 19th century Martin will sell for far below what a pre-war 30's-40's dread will sell for.
It is even more so with historic Spanish guitars...Today a Bouchet or Fleta from the 50's will sell for a fortune ($30-50K +) and yet a 19th century french or spanish guitar will sell for much less than $2000.
There is a very well know Madrid builder who has a really nice collection of historic guitars that had contacted a famous auction house about selling his collection at auction. The auction house sent an appraiser to value the instruments but ended up throwing him out as there was no recognition of the historic value and relative rarity of the instruments, all because the names of the builders were not in vogue.
My interest is not for the appreciation in value of the guitar as it would be better to invest in early 50's fenders...it is to acquire it to donate it to the Spanish guitar museum that I am helping Jose Romanillos to establish.
I am not saying any of this in an attempt to influence or talk the owner into parting with the instrument at a bargain price...it is just the situation with most historic instruments, especially guitars. When you consider that even Torres guitars have sold for less than a very good violin bow does, the disparity in price is very discouraging.
If it looks like European Walnut it probably is. I have seen many Spanish guitars, especially ones from Malaga and Valencia that were built of euro walnut. It makes a good sounding guitar but not an exciting wood. Just as today a Mahogany guitar is thought by some to be a less guitar than Rosewood (thanks to many poor student guitars), Walnut was seem as something like a poor mans Rosewood. The guitar would not be mistaken for a cypress "gypsy" flamenco guitar but was still a fine rosewood guitar.
In the past Valencia was the home to guitar "factories" that would produce student grade guitars with any label you want whereas Malaga was known for having the best french polishers. It was traditionally women who would be given the task of french polishing (as it still is in Mexico today) all based on the excuse that women had smaller hands.
Tough to say what a ballpark for a Lorca would be sight unseen but it could be anywhere from ~$500 to maybe $2000...possibly more but not much more. Its value is mostly to collectors of Spanish guitars. Feel free to give him my email address as I can at least give him some advise on how to conserve it so it keeps its historic value or if he is interested in selling to me or any one else.