Hi Stig,
I must admit in terms of known R.11 serials your serial appears a lot more likely. That is there are a fair number of R.11 with C.55** serials on Albin Denis
http://albindenis.free.fr/Site_escad...te_Caudron.htm For my part the only R.11 serial I have in the C.36** is C.3608 and even then,this is accepting the sellers caption because even with magnification the serial is not legible.
However, I 'm going to send you a word copy of the photo I have just posted which you can magnify (say more than 400%) and which I argue shows the upper part of the first numeral being open to the left and the second numeral appears closed on the left where it loops at the bottom,we both agree that the third numeral is different.
Regards,
Clint