The Papst 412 fan arrived from Farnell today and as expected there is no motherboard fan connector attached so I soldered on a spare 3-pin fan connector so that I could connect it to the P6 (ODD) 4-pin Molex plug (using a 3-pin to 4-pin adapter, of course).
The fan seems to push a decent amount of air, though it's not exactly the quietest fan in the world so I attached it to a Zalman Fanmate fan controller to slow it down a bit and make it silent - I reckon it will still move enough air to keep the PSU in the N36L comfortable. I'd be surprised if the original fan ran at the full bore 7000RPM and would expect it to have been under-volted at 7V or maybe even 5V so probably isn't pushing the rated volume of air, in which case a slowed-down Papst is probably still a reasonable match for the original fan (wish I'd measured the voltage before putting it all back together!)
One rather annoying problem is that the attachment holes on the Papst fan have a diameter of 4.3mm (+/- 0.1mm according to the
datasheet (PDF)), and the supplied HP screws are closer to 4mm in diameter so they don't actually fit and cannot be used to attach the Papst - luckily I had some spare fan screws available with a larger diameter (about 4.5mm) and that sorted it. The holes in the PSU casing itself are probably 5mm (maybe even 5.5mm) so there are no issues fitting the larger fan screws through the PSU casing itself.