74degC thermosat is available from SNG, C28067.
Regardless from what temp rating you get, please do measure the distance they SHOULD open on your car and then measure the distance the thermostats actually open. Latter must be at least 1mm more.
I have learnt with these classics to question almost everything I encounter, by asking WHY is it like this. So very often the answer lies with "emissions". The conclusion being, it was better for meeting the emissions regs applying at that time, but it was not better for the engine (or your pocket). The vacuum retard diaphragm on the S3 is perhaps the best example.
So the question I'm asking in this instance: "Is 74degC better for the engine than 82degC or 88degC?" I believe they all have merits....