Well, I don't know if I can help you, but what you appear to have is as you suspect, an invite to apply for the 76 edition of le Mans.
Should have been 3 sheets Mark, the 30th Novembre letter from Daniel Poissenot, with the PS at the bottom giving the signing on times
Lundi 9 Juin de 14H 30 a 18H etc...
The application form, top left a box Photo Nouveaux commissaires, top right a box, agrafer ici la photocopie de votre licence 2008
Then an application for the classic in July
Good news - you have till March 3rd to apply for the regular 24 hours or the classic.
Bad news - seems you don't do French!
but seriously - if ye want to go - it's an easy enough form to fill in
I'm here all day - severe dose of sniffles has me bananded from work.