I have docs about the much newer Peugeot 307, but it can be useful for reference.
Diesel 2.0 HDI 90CV, well above your car, is homologated to tow 1300kg
Normal 1.4 75CV, a bit above your car, is homolog for 1000kg
Your 1.9 diesel maybe is equiv to 1.2 or 1.3 normal engine, so your homologateg tow capacity is maybe 1000kg or 900kg or something aroung it.
My dear old P205 weigthed around 850kg, your race prep car is lighter for sure, and you will know its weight with precission. Add the trailer and we surely have a very close legal situation.
Conclusion: IMHO look the official homologated figures because it is not clearly below or above your case
I hope this is useful somehow. If someone had the original user handbook for the 309...