I would support the general comments that Alex has made about Thomas' mysterious Rene Herse, and in particular those about the Speedy chainstays.
It is a common practice among French builders..and probably among some English custom builders, to mix tubes sets to obtain the best ride qualities The use of other brands of chainstays, and in this respect SPEEDY and, more recently VITUS, come to mind
Perhaps M Aubague was/is a heftily built guy, given to untidy or extra powerful pedalling styles, so the frame-builder brazed in some beefier stays...or perhaps M Aubague asked for them. It all makes for an intriguing frame
It would be interesting to see photos of the frame in order to ascertain its probable age. If it is assumed that the main tubes are Reynolds 531..and the frame is from the mid 70s.. Reynolds were known, certainly here in the UK, to have certain problems with some of their chainstays, particularly regading the section adjacent to the chainrings.
Claude Auibague was/is a celebrated member of the Audax Club Parisien, being its President from 1991 to 1995, and was responsible as the organiser of the Fleche Velocio until 1996. The Club still has a Trophy in the joint names of M Aubague and his wife, that is awarded for a certain type of team event. I found an account of a cycle ride promoted by the Audax Santa Cruz in Brazil in March of this year. There was a mention of M Aubague, but as the account was in Spanish or Portuguese I could not decipher much more.
If Thomas would like to send me the address stamped on the bike, I will get a friend in Paris to check it out..see if M Aubague is still there. Otherwise I am prepared to write to the Audak Club Parisien if that would help sort matters out.
Norris Lockley..Settle UK